Unhealthy Thinking in Relationships

I have an issue in some relationships where I'll get so worked up I start to just think about ending the relationship so I don't end up hurt. I suffer from BPD and I'm trying to get better with handling it, but sometimes I break out of that healthy thinking stage. I love my boyfriend, but when he talks about leaving for college or anything like that I just feel like he'll just abandon me and I'll get hurt again. I just don't know how to deal with these thoughts and it's frustrating. Does anyone else feel this way? How do you cope with it?