My partner of 3 years, currently broken up actually, has BPD. Originally diagnosed as bipolar and that switched to BPD about a month ago. 

I told them they have to move out and I currently am struggling with that decision. I've caught him lying and using apps to arrange hook ups. He swears he's never actually gone through with it. I do believe that part is true. 

Besides this issue of lying and this behavior with apps, everything else has been a dream. Literally everything I've wanted, which is why the break up was such a hard choice.

I hope that someday we can find a way to work things out and try again. He has a therapist that they are just starting to look into his BPD. I'm encouraging that. 

What else can he and I or just us individually do to help mend the trust that's been broken? What else can I do support him on this path I hope he stays on to better manage his new diagnosis? Any suggestions or personal experience would be help.

I love my partner and this has been the most painful break up I've had in my life. I'm struggling to wrap my head around how it could be so perfect in so many ways, but he could damage the trust in this one area so severely.