I think I love him, but I dint know if he even likes me like that, and he has a girlfriend what do i do?

First advise, if you don't want it to be done to you, don't do it to another girl. Talk to him, have some self respect, from what you say, he is interested in you, but why is he with someone else? I don't think you should ruin this relation ship, if he really likes you, let him realize that he rather be with you, trust me, its not a good thing for you to get in between relation ships, you will end up hurting this girls feelings too.