I want to break up with my boyfriend but a close family member of his is dying. Months ago he cheated, we said let's give it another go. Six months have passed and for me it's just not working, he's showing no interest or effort and I'm pretty sure he is cheating again. but during those six months he's found out that a close family member is dying. I can't break up with him because of this but I feel like then I'll say oh he's grieving so I can't break up with him after.

For context we've been together for 12 years and I'm close with the family member too, I don't want to hurt him but I just can't be with someone who lies and cheats anymore. Any advice?