I think for a second, if you could,
Pretend your mum and your suicidal boyfriend are not in the picture.
What do you want?
That is what you should be considering. In either scenario, you’re being there to support someone, essentially. I would suggest that a person who is so disturbed as to be self harming and suicidal needs to focus on his MH and not romantic relationships.
Your mum needs to sort out her divorce and the house. Maybe you can set aside a certain amount of time to help her figure out what to do, or at least point her to resources. You can’t do it all.
If you want to move to the UK to start your life properly, do that for yourself, but not for the bf, okay? That doesn’t mean you have to cut him off or ghost h8m, but don’t move there, in with him and stay in the same depressive relationship that you can’t fix.