Hi Unicorn!
I must tell you ... .YOU ARE AWESOME! YOU SHOWED SOME B@LLS & STUCK TO YOUR GUNS! BRAVO!
I have done the same thing ... .for the same reason ... .well close to the same thing. ExBPDgf was still texting & calling me & we would talk for hours about deep subjects or other simple things for hours. On occasion she would let me say the night with her on her schedule ... .BUUUT ... .she had a bf. She continued to tell me "I'm trying to break up with him, it's hard, I've never done this before". When I would press the issue on some sort of commitment with us ... .she would get upset, mad, angry, rage, throw a damn temper tantrum & she would tell me I'm in a committed relationship with bf and would kinda blow me off. Then a day or two later she would text, or call and we would engage in conversations and the process would start all over again. Does this sound familiar yet?
SO like you ... .she called one night ... .she started to talk about things and then the conversation turn to erotica ... .before things got to far I asked her if she has these kind of conversations with her bf ... .she said no. I said why not? She told me because he doesn't do that ... .he's vanilla ... .I paused ... .there was a long silent moment ... .I knew what I was about to say was a major boundary ... .I knew it was time for it but it was going to have a lot of radioactive fall out. I told her, " maybe this is the kind of conversation you should be having with your bf". With that ... .her tone of her voice changed to sadness ... .again I"m told, "I'm trying to break it off with him" ... .I told her, "I can't and won't be a part of this triangle anymore ... .if you want to really be with him I won't stand in the way ... .you have to decide to be with him without pressure from me. If you want to be with me ... .then I shouldn't be pressuring you to end things with him ... .it shouldn't be that way. I respect you ... .more importantly I respect myself ... .I think its time to say good night ... .and with that I hung up the phone.
SO like you I set the boundary ... .like you I have to hold the line ... .the next morning I received a text from her ... .words to the affect, "You were right, I was having an affair with you and I feel bad about it. Even if we continue to have conversations (which by itself is a type of intimacy affair) we would skirt around the sex and things would go from there ... .starting to day that will end". So she sees the boundary ... .now what happens if she calls ... .I'll ask ... how are things between you & your bf ... .if it's still an issue ... .I'll enforce the boundary like others have suggested in this thread. Again, it gets easier with each passing day Unicorn ... .
Thanks to this site, my therapist and a lot of reading I've learn to set boundaries with my BPD mother & sister. They have actually called yelling at me asking me if I'm seeing anyone, where am I in the country? and I tell them ... .No ... .my life is my life ... .I will tell you what I want to tell you when I want to tell you. Of course my mom thinks she can bully me into confession ... .and I laugh ... .you're funny mom ... .I'm a grown man ... .do you really think this is going to work ? Are you going to ground me? WOW to funny. That helped me with setting the boundary with the ex gf ... .and you know what Unicorn ... .I feel pretty damn good about things. You have learned to stand up for yourself ... .set the boundary ... .you have learn to respect yourself ... .in turn this will have him or others respect you. Think about it for a moment ... .if the situation was reversed ... .would he respect you? yeah I'm getting a divorce ... .only to find out you didn't?
I've learned to do things without her ... .yes I miss her ... .yes I still care & love her ... .but a boundary is the boundary and if this relationship was going to work it was a boundary that needed to be set. She continues to see her therapist ... .and has decided to see another one who is better equipped to managed DPT / EMDR therapy ... .so she tells me. She has started to go back to church & bible study classes. Will my boundary work? Only time will tell ... .if it doesn't ... .I'm NOT ... .i repeat ... .I"M NOT going to stop living my life.
I continue to ride bikes, hike, work out to help manage the stress all of this causes and I feel pretty darn good. I've changed my eating habits and getting back to where I should be in with my physical & mental health. Hell I've even started watching & doing Yoga on Youtube ... .

I would suggest you do the same in addition to calling old friends you haven't talked to in awhile ... .go out with a girlfriend for coffee, a movie, bowling, a hike or a walk ... .get the heck out of the 4 walls you live in and live your life.
Stay strong! You've made the first step of a very hard journey but it's soo going to be worth it in the end!
JQ