Thanks PinkPig and RainyGrlJenny!
Things are still going perfectly with Dahlia. I recently told her that I love her and she said the same back.

We're planning on visiting Home Country and her meeting my family and friends there later this year. Everything is just going so swimmingly and we're both pretty deep in NRE.
...Which brings me to my other subject. Hank is having some difficulties dealing with the me and Dahlia situation. Outwardly he is behaving well, but he tells me that he often feels bad about the fact that his partner is dating his ex. He feels...replaced I guess. Since Dahlia broke up with him pretty soon after me and her started dating. And I can understand that. He has also told me about some other feelings he's having and some of them really remind me of the time when it was me, Hank and rory in a similar situation and how I was feeling at the time. So I keep drawing comparisons to that and Hank gets upset because he doesn't think these situations have that much in common. And then I feel like he never really understood how I was feeling back then if he can't see the similarities. And so on. We've had basically the same argument several times because we just can't seem to fully grasp each other's point of views. But today I think I realised one thing. Hank keeps saying how it's so different because me and Dahlia have a sexual relationship, which him and rory never had. But thinking back on it now, I remember several conversations with both Hank and rory separately where I said that what had already happened (them getting close, having romantic feelings and spending a lot of time together) is already the "worst case scenario" for me. Whether they decide to have sex on top of that or not is pretty irrelevant to me. For me it was so much more about losing that "specialness", that I couldn't talk to either of them about the other, about integrating bits of my life too much, being left out. None of that has anything to do with sex. I genuinely believe (although cannot know for sure) that it wouldn't have made the situation much worse for me if they had had sex. Whereas with Hank it seems that sex is exactly the thing that makes the most difference here. That is the thing that makes him feel the worst and the thing that makes him think these two situations are so different. So he thinks he has it "worse" than I did back in the day because now there's sex involved. But what he's not realising is that for me that never mattered. So basically if I put myself in his shoes in the current situation, I think that I'd have pretty much the same set of feelings I did back when it was me, Hank and rory. Whereas when Hank puts himself in the shoes of past me, he thinks his feelings about that situation would be very different to what he's feeling now in the current situation. Which is why he doesn't understand/like it when I compare the situations. Comparing feelings is usually pretty futile because they're so hard to grasp, but I think this revelation just helps me understand both him and myself more.
When it comes to Fay, things are going pretty well with her as well. We see each other usually about once a week and we really like each other. There are a couple of things that I sometimes struggle with that make me think that maybe this relationship is not meant to last forever, but then again, who cares, right? I'll just try to enjoy it while it lasts.

The issues we have have to do with sexual dynamics (her being gray-asexual who does have sex sometimes with some people, but with who and how...it all gets pretty complicated) and some differences in how out of the closet we want to be. She has a primary partner that she'll marry next year and everyone knows they are together. She's not as out about her other partners, and that has potential to bother me a lot. I've had this hierarchy problem with at least two partners in the past, but it's the kind that I can't really see properly from the start, because I always understand that people don't want to be out about something that's just developing, that's not really serious yet. So I always wait until we've been together long enough to warrant that step, and sometimes it turns out it's not a step they want to take at all. So we'll see. It's possible that I'm just worried for nothing, but I guess I have some baggage around this.