How to get this guy to like me back?

i'm so confused because there was this guy and i am really good friends with him , but now he has a girlfriend and she is really ugly and fat but thats what he likes i suppose but the other day i was on the trampoline under this cover and i pretended i was a monster and i grabbed him and he kinda shouted out i love you and i said what and he mumbled it away as if it was something else.lets say this guys names (robert) and sometimes when i see robert he now always talks about his girlfriend everywhere its making me sooo jealous lets say her name is (steph) and he is like " ooohh i miss steph " ,, " im going to the cinemas with beth" and it really annoys me , but yet again he pretends to kiss me nd that?? im soo confused?