trip confusion???

So I just got back home in New Zealand from japan and what a trip! So I'm there with a group of mates and a dude in our group was aaaaaaall up in my business, holding my hand, hugging and kissing me and all that. So I talk to him like 'uh what's going on here', then he goes on about how pretty I am and that he likes me and wants me. All I'm thinking is, okay, I'll ride this wave. Next thing I know he says 'I don't want this 'relationship' anymore'. Uh Wah? Relationship? When we're we in a relationship? Whatever though, didnt worry me. Anyways, long story short, he pretty much tried to get with all the other girls on the trip. He didn't succeed. On the last night (BOMBS DROPPED) we found out he had a girlfriend the whole fkn time. What a lad. Now I don't know whether or not to tell her what happened???