What does it mean if a guy really likes you but seems afraid to approach you and gets very obviously jealous when he sees you talking with other guys?

It is possible that there is a feeling of insecurity in the fellow, and for him to get obviously jealous at the thought of you talking to someone, may lead to being over possessive if a relationship does develope. I suggest caution the best policy here. actually talking to another MAN would probably be better to say than talking to other people.