HI hardtimes,
I"m so sorry that you are going through such a difficult time. I think it's great that you let your W know that it is not ok for her to sleep with other people if she wants to work on things. Having BPD may contribute to her having a hard time with relationships, but it is not a full excuse. She needs to know how her choices affect you.
I think there is hope for you but it will take a lot of work. Have you thought about getting T for yourself too so you can work through whatever issues arise from being in a relationship with someone with BPD. It can help you with boundaires, asserting yourself, and general coping.
Do the therapists you found specialize in DBT therapy for personality disorders? What will you do if she decides to not go to T?
I'm definitely considering therapy for myself as well for all the reasons you've listed. If she doesn't decide to go I'm not sure what I'll do. Maybe if I learn better ways to communicate it'll make a difference.