Where have all the gay girls gone?

So, I'm getting ready to go to a friend's wedding this weekend. She's marrying this really great guy and seems to be really happy. The thing is, she's yet another one of my friends who used to identify as a lesbian. That makes five, count 'em, five former lesbian friends getting married to guys. This will be the third wedding I've been invited to, only one was an ex (oddly it was not as awkward as I thought it would be). Two bi friends have also gotten married to men in the last few years. Out of a loose group of ten of us lesbian and bi women, there are only three left who aren't married to men. A lesbian a bi woman and me (also bi).

I'm not complaining, at all, really. I'm glad my friends have found people they truly love and want to make a lifetime commitment to. I'm just a little surprised, I guess, and am also trying to figure out my own changing preferences. I have always been bi, but for years I was exclusively in relationships with women. That changed a couple of years ago and I started noticing guys again, and more. I'm in my late twenties now and I'm wondering if my biological imperative is starting to make my mind up for me. I really want kids someday, and the sooner the better, honestly. And, while I know in my mind that I could be with a woman and have kids, it's like my genes or something are telling me different. I used to be a 75/25 (at least) bi, women over men. Now, it has reversed itself, and I find myself noticing guys when I never used to. At the gym or on TV or in magazines. And I find myself sort of unmoved when I see a beautiful woman. Has anyone else felt like this at all?