Nursehope, I am so sorry you find yourself in such heartbreak. It sounds like there is a lot going on here,and I hope you find a place of peace soon. There's a lot of good advice on the boards, and wonderful people who've been through what you're experiencing.
First things first: stop comparing yourself to her, or to anyone else. You are you. Work on finding your love for yourself again, on finding your confidence from within who you are, not by comparing externals. The reality is there is always someone more beautiful than we are out there (and "beautiful" is such a subjective terms as to be almost meaningless anyway), or smarter, or richer, or with a higher libido/kinkier, or more successful at their job, or whatever. Relationships shouldn't be a competition, and viewing them competitively can make poly very difficult and unhealthy. There are many things that make up a person, and your husband clearly valued many of your qualities enough to fall in love with you and marry you. Don't measure yourself, or your relationship, based on someone else or their relationship.
Next: there are some clear communication problems here. Before I dive into more, can I ask how long this Triad/Vee (it's hard to tell which it is, really) has been going on, how long she's lived with you, and if you and she are involved? Are you enthusiastic about poly, and dating on your own, as well? And, how was the marriage before you opened it?
It sounds like your hubby has a bad case of NRE, which happens a lot. He needs to own this, and step back for a minute to evaluate what each relationship needs. This may be difficult for him, and it wouldn't hurt to have him do a bit of reading on the topic. But, it is up to him to act like an adult with prior commitments as much as it is for you to be responsible for stating your own needs.
Letting the rage, jealousy, and resentment build in you is a huge recipe for disaster in so many ways. It might help to stop focusing on their relationship. Focus on your own. How he looks at her, what they do, etc. has no bearing on his relationship with you. It's clear your needs aren't being met, and that's going to continue to cause resentment. Solving that issue is much more likely to bring about a positive change. It sounds like it's time to sit down and have a real conversation about that.
Determine what you need from your husband (and your girlfriend) to feel safe, secure, and loved, and communicate this to them clearly, as well as to ask what their needs are in all this. Think about these things carefully, to make sure they're about you and your relationships and not about controlling or changing theirs. So, for example, perhaps you need more time with your husband. Ask for it, and state it clearly: "I need three overnights a week with you, and one of our days off, so we have time to build and strengthen our relationship, do the things we enjoy, and stay strong." Or, "Because I have much less available time to spend with you due to my work schedule, I'd like to ask for more of the time I am at home to be spent as a couple. It would be helpful for me if X time to X time was set aside for you and I, while you and she have X time to X time while I am at work."
Understand that there is also the GF and your husband to consider, who will have needs of their own, as well. And, don't go for "equality." Relationship needs and priorities are different for everyone, and will change with time and situation. Don't try to make everything "equal," but, instead, work on lovingly meeting each other's needs. Some people need more emotional time, some more sexual time, some more activity time, some more overnights, some more help around the house, etc. So, while one partner may need more sex to feel connected, another may need more time out doing various couple's activities. I am very independent, for example, so tend to need less time than some of my metamours; but, I generally need more sex than most of them--it's how I stay connected. It's up to the three of you to find a balance that works for you all, that is healthy, and that isn't intended to harm the other relationships.
Try to reframe your thinking and your wording. Poly isn't about who someone wants more--people are different. Your husband isn't going to want to be with you the way he does her because you and she are different people. He will want to be with you in the ways that your relationship works. It's not a matter of "more," it's a matter of differently. That is the wonderful thing, or can be, about poly--there are many wonderful people and interpersonal dynamics in the world, and you get to experience them in different ways.
Could he leave you for her? Of course. The reality is, anyone can leave anyone at any time for any reason. But, that happens all the time in mono relationships, as well. It doesn't make it hurt any less, but there are never any guarantees of "forever after," despite what our culture's overly-romanced pop culture wants us to think. It is wonderful when people can spend a life time growing together, of course, but that't not the only measure of a successful or wonderful relationship. Living in fear of it won't make things any better. Express your concerns in a helpful way "honey, I want to grow with you, and am concerned our lack of time together is causing us to grow apart. I would like to work with you on re-building our intimacy. Can we talk about that?" And, understand that you cannot control others. The best thing you can do, for yourself and your relationship, is to let go of the jealousy and fear (i've been there, and know it's so very, very hard), and find your own things to love about you, things outside your relationship that you find fulfilling and enriching, things to bring back and share with your partner that keep the romance fresh and new (this doesn't have to be sexual exploits--a travel group, a book club, a hiking crew--something YOU like for YOU).
Are these things you could discuss as all together, to get everyone on the same page?
So we've got the whole triad relationship going and things were ok for a while. I fought my jealousy and insecurity tooth and nail but to no avail, and I find myself growing increasingly bitter. I watch my husband and my girlfriend do all the things my husband and I used to do when we were dating, I watch his eyes light up when he looks at her but never see that look directed toward me. The short version is that I'm watching my husband behave like a newlywed with someone else and it's close to destroying me. I feel that I am being replaced by her. She is everything I'm not. Beautiful, super libido, interested in all the same things he is and, as far as I can tell, meeting all his needs splendidly. I have raised these concerns to him and his response is always the same, "you're not being replaced, neither of you is replaceable, I love you." But I find that his actions don't line up with his words. When there is a choice between being with her or being with me, he is always with her. When I bring this up he apologizes and says that he'll try to make sure he spends more time with me, bu t I want to scream "YOU'RE MISSING THE POINT, IF YOU HAVE TO TRY THEN IT SORT OF PROVES MY CONCERN. I WANT YOU TO want TO BE WITH ME AS MUCH AS YOU DO WITH HER!" I'm just not sure what my role in this relationship is anymore. All this is compounded by the fact that I work 12 hour days most days of the week while she works from home and can spend more time with him, and that we all live together so all my off hours are basically spent watching from the sidelines while they go gaga over each other. I feel that there is nothing I can do to keep my position from being eliminated, as it were. I know my husband is tired of hearing me complain when nothing he says will reassure me, but I'm drawing into myself, preparing my self for when he inevitably--in my mind--just leaves me for her. I realize that to all you experienced polys out there this is nothing but a childish temper tantrum, but I could really use some insight.