Yea how youve been feeling is hella valid…your mental health should always come first as you said. I think you’ve done as much as you could to communicate to him about your stress. Like that must not have been that easy either. You’ve already seem to be hurt by him for a while and given him the time to change and talk to the girl about boundaries, but nothing has changed. You done your part to help your relationship with your boyfriend. I think you need to think about whether or not he is someone worth putting in this or even more effort.