What's with the mixed messages?

That is right i asked that question. I ask it because, there is a boy I like and 1 day he will be all over me and be really sweet and kindv'e put his arm around me. The next day though if we are playing a game he will go after another girl all the time and not care about me but, that 1 girl so I ask what is up with him? i guess guys are just weird people and girls should maybe try to avoid at all costs?