Okay, so, I posted this in /r/relationships but I'm going to post this here also with more info.

I have BPD and my boyfriend is my FP or favorite person and it is adding an additional layer of complication to this already complicated situation because my abandonment fear is ranking higher in my brain than how I feel about anything else that has transpired. I know he's been treating me badly behind my back, but to my face, he has basically been the perfect boyfriend. I don't know what to do here. I don't want to break up with him (probably because he's my FP) but he's lied to me so much and I know this would be a deal breaker for other people.

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I (29F) started dating my boyfriend (32M) at the end of June (so about 5 months now). We have a lot of history though and we used to date about 10 years ago. In July, he said a lady friend of his had to crash at his place for a few weeks. I said I was cool with it as long as they had NOT slept together before. He said they were never involved like that. **This was the first lie.**

Around the end of September, I got paranoid and found videos of them together that were incriminating on Instagram. I asked him about them. He admitted that he had lied to me and they had sex on the previous New Year's Eve, when we were NOT dating. He said he had seen her a few times after that but made it sound like they had only hung out after once or twice. The videos were from January 2019 so it checked out. I was angry but told him that it was the time to be honest with me about everything. He said that was all of the information and they had only had sex once. **This was the second lie.** He kicked her out on October 1st.

Fast forward to last Saturday, I am with him and some old mutual friends at an arcade. I end up talking privately to one of them and they end up telling me that he was actually involved with her for much more time than he originally admitted. So I confronted him at home once we left... and he admitted that they had actually been FWB from January until June (a few weeks before we started seeing each other). He says he ended things with her and that he did NOT sleep with her while she was living with him. **I don't know if this is a lie.** I feel like I don't know up from down any more and I don't know how to proceed with this.

I want to believe him but it sounds ridiculous that he would have a FWB situation for 6 months and then STOP sleeping with her once she MOVED IN temporarily for 3 months.

I don't want to break up with him because this is the best relationship I've had, aside from the lying that has been going on about this chick that he no longer speaks to at all (which I am certain of). But I don't know how I can possibly trust him after he's lied so much. He said he lied because he is afraid of losing me. He suggested that we got relationship counseling but the only problem is that he has continued to lie to me.

\*\*TL;DR: My boyfriend lied to me a lot, probably cheated on me and I don't want to break up but I don't know how to trust him any more. He says he lied because he doesn't want to lose me.\*\*