Answer: You can't - and, arguably, shouldn't - trust this or any other boyfriend until you trust yourself.
Not that all guys are bad, obviously. It's just that getting into a healthy relationship requires more than just two decent people finding each other (i.e., people who feel obliged to be good to others for the sake of it). It also takes honesty, confidence in your ability to read your situation, and a pinch of skepticism - not so little that you rationalize every bad thing you see into the best-case scenario, and not so much that you're chronically jealous, suspicious, or fearful.
Keeping your equilibrium when you're with this person will require either a healthy outlook on your part, or a very forgiving one on your partner's. That's because people who aren't confident in their ability to read situations accurately - i.e., people who don't trust themselves - tend both to rationalize away serious problems, and to overreact to minor ones.
Since your confidence is shot, I suggest you concentrate on building it back up by trying to make sense of all those [jerks] and their antics. You want to figure out what role you played in choosing and trusting men who went on to take advantage of you.
Since it's hard to have perspective on yourself and your past while you're dating someone, consider recruiting outside guidance through your college's health services.
Otherwise, you'll have to exercise the discipline to take a self-guided tour of your own frailties, by looking for patterns in: the men you seek out; the urgency of your searches; your behavior with these men; the behaviors of theirs that you put up with or explain away; your emotional habits growing up; the habits you observed in your parents. Figure out when you under- and overreacted in the past, to what, and why.
Don't be afraid to bring in ideas that seem unrelated - for example, your attitude toward school or achievement or friends or money or general conflict. These provide clues to what you care about, where you seek happiness, where you actually find it, and what trips you up along the way.
E-mail Carolyn Hax at tellme@washpost.com.