Thank you, thank you, thank you!!!
I just want to say thank you again to every single person who posted replies to my threads and helped me get through this. You each offered a unique perspective that really helped me keep my wits about me and not get lost in my emotions.
It has been a little more than a week since Leaf broke it off with me. He really has no idea what to do next though. He didn't have a plan for after the break up at all. He makes about $300/ month right now working part time. I asked if he intended to move in with Flower - he says he doesn't know, never asked her about that. He spent three nights with her after he dumped me and when he came back he still didn't have an answer. So I told him he has until Oct 31 to figure it out. He's either paying 50% starting on Nov 1 or his stuff will be on the front lawn and the locks changed. I already have a good friend who wants to move in with me so he's really in my way right now. I have my appointment at the bank already to get our money separated and begin the divorce process - because yes, this is really more like a divorce than a break up. Frankly, in a financial sense this is going to be the best thing that ever happened to me - and maybe in some other ways too.
Leaf still wants to be friends.

BEST friends, he says. We will still spend lots of time together and love each other as friends. I'm not gonna lie. I like the idea of still hanging out with him and having him in my life even if he and I aren't a couple. But I am approaching that with caution and not getting my hopes up too much. I can't imagine his new girlfriend being okay with him having a close relationship with me. She wanted his heart to not be "divided" - that is what she asked for. But it still is divided. He still loves me. He's still attracted to me. The more he and I hang out I suspect, the more she will restrict our relationship. I absolutely will NOT stand for that though. Only Leaf and I should have control over our relationship. I never made rules for the two of them and I won't live under her rule. He has made it clear he really doesn't want to lose me entirely and if she ever asked him to cut me out he would say no. But I will cut myself out if she starts trying to control our relationship and he can suffer the consequences of his choice. I refuse to let him walk all over me to please her. I am not a doormat. Even as friends I will expect certain things of him and if my needs are not met in our friendship then he will be on the receiving end of a break up next time. And I mean that.
I should clarify - Flower actually didn't ask him to break up with me ever. Flower said she couldn't continue in that kind of relationship. She bowed out, although very reluctantly and probably hinting that she wished she didn't have to. Maybe that was a manipulative way of getting what she wanted without looking like the bad guy. It was entirely Leaf's decision to keep her from leaving by doing what he saw as the only solution - dumping me. I asked him once if he could just be her friend and he said it felt like it should be more. When he told her he would do whatever it takes to be with her she was, understandably, very happy. So once he made the decision himself to dump me it proved to her that she should stay with him.
Humorous aside: Flower's best friend and roommate is going through a breakup right now with a man who cheated on her. Leaf mentioned this to me and said that parallels in the two situations are making it really hard for Flower to trust him right now.

SERIOUSLY!! You think?!?!?!
Leaf says Flower feels very insecure about their relationship and she's scared of getting hurt. Breaking up with me was his way of making her feel better about her insecurities. I pointed out the flaw in this logic to him: you didn't just prove to her that you will never hurt her. In fact quite the opposite. You proved that you can leave your partner of nearly 10 years (someone you still claim to love) for the "other woman" you have known for six weeks. I think that would make me feel even more insecure if I were her. I sure wasn't secure in my relationship with him. But she has probably convinced herself that he loves her more than he ever loved me. I know that's not true though. Once upon a time he loved me with as much passion and reckless abandon as he loves her with right now. It's only a matter of time.
They have gone away together for the weekend again. This time to the wedding of one of Flower's friends. He has promised to talk with her about their relationship and what she expects from him now on this trip and come back with some answers for me.
I suspect as more of the details come to light and he figures out exactly what he is choosing it will sink in. He will have to compromise some parts of himself to be with her. He and I both fundamentally believe that love should not be restricted. You can't control who you love and I would never ask someone I care about to pretend they don't love someone or ignore their feelings to prove their love for me. Freedom in love was central in our relationship. I know he still believes in that. He says he can be flexible on those beliefs though.
He barely talked with Flower at all about what she wants from a relationship with him and what her boundaries are. He made a very rash decision. He says he is willing to bend on his ideals in order to be with her - but how far and for how long? It's easy to say you can change for someone, but in practice it's a lot harder. He actually had the balls to say to me that he hopes one day I will love someone so much that I would do anything for them - I actually had to restrain myself from punching him in the face for that one. I am not a violent person.
Meanwhile I am moving on with my life. I have a fantastic group of friends and family who are helping to distract me and lift me up (I include you message board friends in this group). Even Leaf's own mother told me she is sorry and that her son is a "fucking asshole." I am getting my ducks in a row money-wise. Like I mentioned already, I have a very close friend who wants to move in with me when Leaf gets out of my house. I am glad I won't have to be alone all the time. I am not waiting for Leaf. I already had a casual relationship started with another man before Leaf and I fell apart. I'm not jumping into another serious relationship with him, but I do enjoy spending time with him and I'm excited to get to know him better.
I wish only the best for Leaf and Flower, but I can already see some serious relationship issues that the two of them will have to overcome. I don't hope they will fail, but I honestly don't see it working out for them. Maybe I'm wrong, but I know Leaf - he will bend over backwards and give her the moon if he has to... for a while. But he has a selfish streak in him and a stubborn attitude when dealing with other's emotions. I put up with this for at least the last five years of our relationship - maybe she will too.
I think I've come full circle now. From thinking I couldn't live without him - to thinking I will be better off without him. If Leaf ever does want to come back to me I will have to think really hard about it. He says after he and Flower are together for a while and on more solid ground that he would like to be Poly again. At which point he and I could be together again. I really doubt that will ever happen. I think I would take him back if he and Flower break up, but I could never trust him to be the hinge in a V with Flower and I. I don't think he has what it takes to be a hinge in ANY relationship, but especially after what the two of them have done to me - it will never happen. And Leaf and I will NEVER join our finances again if we get back together. I don't think I'll ever do that again with anybody. Leaf would have a very long way to go to regain my trust, and my expectations of him would be higher than he is used to.
This has been a fantastic learning experience for me. My strength of mind and ability to maintain an inner calm are being tested to their limits right now and I am succeeding (most of the time). I have always been a confident, independent, and strong person - that was kind of shaken lately but it's coming back to me full force. I am thinking about MY future, not OUR future - and it looks bright for me. I have been set free. I should have done it myself, but I couldn't. I might have stayed in that leeching relationship for the rest of my life if this hadn't happened. I guess I really should be thanking the two of them.
Thank you all SOOOO much. Keep doing what you do. You folks have a lot of wisdom and compassion to share. I can never thank you enough.