Hi, I just read your post and think that you should go the gp and TELL them you want to be referred for Cognitive behavioural therapy, It deals with ways to stop negative thoughts or talk yourself round from them!
I had very bad anxiety but did not want to take any meds for it, and i had one course of CBT and am pretty much fine, and that included dealing with my ex ending our relationship which i found extrememly difficult.
Also with CBT you can get the opportunity to talk about why you are having these thoughts, I also had PTSD and have self esteem problems too so being able to talk to someone else really helped with that too! I now find it easier to not think everyone is going to leave me and everyone secretly hates me etc etc....
I really hope this helps!! and Im glad you have such a supportive bf!! xx