I feel so sad for you. I've had 3 MCs, luckily all complete so no ERPC needed, but nonetheless sad for that.
I felt, reading your post, that your girlfriend had actually started to move on before your MC, that she liked the road life of a muso, and that she was starting to regret being "tied down" - so for her, the MC was more of a relief (sorry) because it got her out of an awkward situation. Which is why she was so heartless about it, and why she made the decision to fuck off so quickly after it.
Horrifying for you of course! But I think probably better she did it now? Give you a chance to settle into being single.
Now, you're trying to get pg again and doubting this is a good idea. Well - ask yourself the only important question here: Do you want a baby?
It seems you do - and you have a willing donor who doesn't want to be involved as a parent (could be a bonus, tbh) - but what you don't have is a loving partner who wants to be a parent either.
What I would want to know from your exGF is whether the "baby thing" is the reason she's split from you; or whether the baby thing is irrelevant. If it's because she doesn't want a baby but knows you do, then you decide what is more important, her or the baby.
If it's nothing to do with the baby thing, then all you have to do is decide whether you want a baby, and whether you can do it alone, and make the split permanent.
TBH I don't think she's being fair, keeping coming back to your place to stay over. Why is she doing that? You really need to sit down with her and have a deep heart to heart, before making any decisions.
And while I understand your "weirdness" with the gay donor friend, don't close that door completely until you know what you're doing. He'll probably cut you some slack because of your recent losses, but it won't last forever.
Good luck - I do feel for you - allow yourself to grieve your loss properly, and if it's helpful to you, maybe buy yourself a little keepsake for your angel baby. I have 3 tiny crystal angels. x 