Hey there,
I had a roomate who seemed to do the exact same things you are doing. She had trust problems with her family, her boyfriends, and even with me. In the last three years she has had three dramatic breakups, barely talks to me, and refuses to acknowledge her mother. I know she was on anti-depressants, but she stopped taking them when we started living together. If you are taking any anxiety/depression medicine, don't stop! At least not right away. And if you're not taking any, perhaps you should talk to a doctor.
I too have anxiety problems. Last year I was diagnosed with anxiety disorder and ADHD. I get really panicky before I take tests, and right before the LSAT I had a panic attack. This led to a lower score than my practice exams, so I finally decided to see a pyschologist. (It really helped.) He taught me how to physically relax my body when I get anxious. My regular doctor also prescribed Adderall and Prozac which have both helped immensely.
Right now I'm in law school, and the level of stress is unreal. I understand that my situation is much different from yours, but after talking to my doctors, I've learned that anxiety and stress can have an effect on different aspects of life. For you it's your boyfriend; for me it's school. I promise I feel just like you when you say, "I just want to be happy all the time and so much less stressed out!"
Here's a few things that have helped me in the last year:
medicaton
half-year of counseling
yoga
talking it out with close friends
Don't make the mistake my old roomate did when she started fighting with her ex-boyfriend. She loved the guy but started picking fights when she didn't trust him. I know she misses him, and her life seemed to fall apart for a while.