this girl could be his SISTER or his COUSIN or even his FRIEND! stop jumping to conlusions and generally being a jealous possesing ho. and dont we get the right to know who the hell you're talking about? is this your boyfriend? your husband? your fiance? some random guy your madly in love with? your BROTHER? you ARE cheap and FAR from normal.
try asking HIM (?) who the girl you saw him with, but dont even THINL of accusing him or asking in an accusatory (is that a word) tone of voice.

Im' sorry about your problem. I will be your fiend.

Did he flip out?

HO!

So wait, you're saying that your boyfriend is sometimes in contact with one of the 50% of the population of the world that's female but isn't you? Well, gosh, dump him right away! He should've stayed in the male part of town, I guess. He shouldn't have gone crossing those railway tracks to girltown if you weren't there to meet him, right?

Don't get me wrong, if when you say he was with another person, you mean "with" another person, fair enough, you need to dump his ass. And better have seen them kssing or more.

But if you just feel you can't trust him to be around another woman without assuming the worst, then frankly this relationship might be doomed regardless. Half of everyone out there is going to be someone of the opposite gender to him. He could not avoid them all, and shouldn't be expected to. So if all you saw was him walking down the street with a girl, and this is your reaction, you need to either grow up, or break off this relationship until you can be more mature.

You are so cheap