Whether or not to trust again after being cheated on once?

This is the first serious relationship i've ever allowed myself to get involved in b/c i've always been too scared of getting hurt or being cheated on. I've been with my boyfriend for six months and we're both pretty sure we want to get married someday.. however.. he recently confessed to me that during a "break" we took four months into our relationship (i needed some time) he was really upset about it, ended up going out one night with some friends, getting drunk(which he never really does) and kissed another girl. He, of course, admitted that it was wrong, and said that he told me because he wants any future we might have to be based on total honesty.. but then why would he cheat on me in the first place??? I know all of the standard "of course if he cheats once, he'll cheat again" responses and i don't want to just be another girl who refuses to see clearly because of "love".. anyone have any advice or another perspective??