Araid Of Being Loved

i have never been in a proper relationship that has lasted over a month... whenever things start to look good or are going well, i find a reason to end the relationship, and the guys i choose are never really people i feel strongly for anyway so i feel no remorse when i end it. I then spend the next few weeks - sometimes months - hooking up with whoever i just broke up with, making sure it never goes into the realms of a relationship, keeping it purely physical.
The thing is, i have now fallen for this properly lovely, sweet guy, but i'm afraid to get to close to him because i KNOW i will end it, or do something to mess it up and i know i couldn't live with myself if i did that to him, but I have a really bad feeling that it is an inevitability...