How do i trust him again?

i found out my bf was attracted to another girl and he didnt do anything about as in he didnt tell her he had a gf and hung out wit her it until he got caught, he said nutin happened n i believe him after alot of snoopin of course. anyway i love this guy so much, and i decided to give him another chance. how do i learn to trust him again. all ihave on my mind these days is where is he? wats he doin? who is he with? it hasnt been that long since i found out about this issue and all before that i neva thought he could do that to me. ide been with him for over a yr. and yea well it sucked big time wen i found out wt was goin on,