BPDFamily.com

So she's cheating on me and I'm done with this. Should I tell the other guy about us. Good idea. Bas idea?

Hey XXX you don't know me but I was XXX boyfriend for quite some time until Saturday morning when she continued a fight she picked on Thursday and left after a long fight and search for her keys (an obvious tell for her lying or doing something that will hurt you is she always picks a fight or pulls away and then blames you before she does it and then accuses you of doing what she is actively doing).  I found your number on a piece of paper in her car a couple weeks ago while we were driving down to go biking at Pebble Beach. I debated texting you for a while and decided you deserve the truth as well and that I'm not making a spiteful choice as Im totally done at this point. I found out about the two of you a few weeks ago while I was staying home to take care of her Lyme disease from a tick bite she got while waiting to see a concert with you and was on her computer. When confronted she then assured me she ended contact with you. We then spent the last few weeks together including going to xx for a 3 day weekend together with her family. This number will only be active for about a day if you have any questions or want any proof.

I don't think you should bother, he will find out who she is sooner or later.
 Also he might not even believe you and he might think that you're doing that so you can keep her. It just doesn't lead to anything productive. She will convince him that you're doing that to destroy the relationship so you can get her back. She will find a way to make it so that she's the victim. I just wouldn't mess with that. The best thing you can do is disappear from her life. Block all contact, as hard as that sounds that is all the respect you have left in this. You have to choose your dignity over  her. She isn't the first and the last BPD patient who cheats. I cannot recall one case of BPD that has not cheated. I know that sounds extreme but even my ex cheated "emotionally "which I  still consider cheating.  I tried to forgive it, but I couldn't. I know it is the hardest thing in the world to withdraw all attention from this being. But I think you owe it to yourself to win your self respect back.

Perfect thanks for the reply. Yes I'm going to leave it as is, and just start my recovery.

I know that her cheating is devastating. The only advice I can really give is try to think of it in a clinical sense.  With BPD it seems that cheating is part of it. Like another symptom.  Don't projected on yourself as if there is something wrong with you or that the person she's cheating with is in some way better than you. I learned first-hand contacting your replacement does no good. As long as he's an enamored with her he's going to take her side so I agree with the other poster. Preserve your dignity and self-respect. You work on you and Recovery. Good luck to you!

Agreed. Respect for yourself is the ONE thing you have that she doesn't and will never have. Leave while you have it. RUN. Block all contact. Do not spend another ounce of your energy. It's almost like a monopoly card but where you get freed from prison, instead of being sent there, except you don't get to pass "go" instead you must go straight to another dimension and never look back. Take what is still intact and leave.
I can honestly say that I am so incredibly thankful that my BPDex did not get my dignity - and let me tell you he tried, oh did he ever want it. He tried to cheat on the replacement with me. AND I said no, AND I went NC.  Getting involved in their love triangles fuels them because then they get to gang up against you, or be the victim, with the help of the other. Do not play in the triangle, it's a trap.  Trust me - you have the advantage if you still have your self respect.