yes i feel what you mean.
its common for me.
if you believe that he is the right one the go for it.
you dont want to be the one who didnt hold on and lose it at the end when you realize that you wanted it in the first place.

@my beautiful friends~ yeah...he confessed to me a while ago. he does show it sometimes. he would ask me out and stuff~ and valentines day he gave me something~ My friends tell me that he isn't the right one for me though..><

Firstly, don't think too much arasso?
Since you feel down when he's with other girls, you might like him a little. But maybe it's just from disappointment (Take note: Disappointment IN THE GUY.) because he told you he likes you,(Did he? o.o) but then he goes and hangs out with others.

Man, if I could bold my writing I would. LOL
But yeah, BE CAREFUL DONGSAENG! ; A ; DON'T GO FOLLOWING BAD PEOPLE! I'm joking. xD ♥

CrazyWriter17 is right~
How do you know he likes you? And "like" as in what sort of like?
And work out if you like him or not~ It will make things easier :]

Don't think about it too much and if you really want to find out some answers then just ask him straight out! :))

I have felt the same way before..

First of all, how do you know he likes you? Did he confess to you?

Well, when one person confesses to someone he/she likes you somehow gotta be cautious especially when you like that person too. You can't say you like someone with only by words and with no action. If he really does like you in anyway he'll prove it to you than just sitting there doing nothing..
try asking him for yourself..