Impregnated Lesbian Couple

So when I was in College I met this really cool girl, we both played basketball for the school and had the same group of friends. I definitely had a crush on her for a while but turns out she was a lesbian, so I respected that and we just stayed friends. After we graduated, we went our separate ways but always kept in touch. About five years after graduation I moved back to my hometown (where she was still living) and I reconnected with her and her fiance. They were both super cool and so we all started hanging out a lot. Not long after their wedding, they started talking about wanting kids and trying to find a sperm donor. One night I jokingly suggested that I would be their sperm donor, since they said they wanted their kid to be tall, like sports, etc.

Anyway, about two weeks after that conversation they asked me if I was serious and I was kind of shocked at first because initially I was kidding. We talked about it more and they said I would obviously have no obligation to be the child's father figure or anything like that (not that I would've been opposed). So after a few months of thought, I agree to it and we end up going through the whole process of me donating my sperm and all of that. Long story short, that process just wasn't working for them. Now THIS was the part that really caught me off guard. My friend approached me and asked me if I would be willing to basically have sex with her wife to try it the natural way. I was floored. I knew that her wife had been with men before, but it just seemed like I was living in a dream that this lesbian couple was asking me to have sex with them. I wasn't sure about it at first, but after getting consent from both of them, we tried it.

So the first two times were SUPER awkward. I basically just went in their bathroom and jacked off until I was close, while those two got each other ready on their own, and then i just stuck it in her wife and came. But the third time was...interesting. So the wife texts me telling me to come over to try again one day after work, so I went over there prepared for the same situation. But when I got there, my friend was gone, and it was just the wife. She said she hadn't felt comfortable doing it around her wife and wanted to try it just us. I was SUPER uncomfortable at first because obviously this is my friends wife and I wasn't sure she would've been okay with us messing around behind her back, even if it were just for baby making purposes. Lol anyway long story short, we ended up full-blown FUCKING. I mean, things went from zero to ten pretty quickly, and this girl was ready to get down and dirty lol. So we ended up fucking four more times (secretly) like that and a few weeks pass before she finds out she has a positive pregnancy test. My friend and her wife are so excited, and although I'm glad I could help, I feel guilty AF that we never told my friend what was happening.

So now my friends wife is almost seven months pregnant at this point and she has been ALL over me. Like literally this woman texts me everyday while I'm at work saying nasty things, wanting to fuck me again. I should state that I haven't had sex with her until before she got the pregnancy test, but I feel like an asshole because I definitely want to. But mostly, I'm not sure why this woman wants to keep fucking me when she's married and is about to have a kid (my biological kid... which is also screwing with my head more than I thought it would). Anybody have any suggestions as far as what I should do about this?!