It seems like your thoughts are very clouded by emotions right now (not saying that's a bad thing; probably feels like being a teenager again). Are there any non-emotional reasons that would have bearing on a potential relationship with either woman?

Do they/you have kids? Is that a problem? Do they/you want kids? Is that a problem? You say "moving quite fast." Is that a problem? Is she gonna be pushing for marriage and you're not a marry'n type of guy? Are there religious differences? Large income disparity? If you date your crush, will your soon-to-be-former-friend be a problem? Speaking of that, how good a friend? Cause he's gone. That's the price you're gonna pay. Is she worth it? Are you more attracted to one of them? Why did your crush and your soon-to-be-former-friend split up?

If one of them has a deal breaker but it just hasn't become an issue yet, then maybe you should consider that when deciding. Like, maybe there's no point in continuing with your GF anyway if she wants kids and you don't. That might make the choice easier. Alternatively, if your crush has 3 unruly brats and her ex is the type to seek vengeance for your (perceived) betrayal, then maybe you leave that situation alone.

If that kind of analysis doesn't help, then I would personally go with the crush. Mainly because "wonder the rest of my life what could have been" fucking sucks, but also because you (should) know her better. You've presumably spent time with her over the years. You already know a little bit about what she's like as a SO from your observations of her interactions with your soon-to-be-former-friend. Assuming you liked what you observed, then maybe she's the right choice. (Obviously this goes the other way too: if you didn't like what you've observed or she's a cheater or something then you should also consider that. Also consider the reason for the divorce; if it was due to her actions, then it's not likely her behavior will be any different with you.)