Just pay attention to his actions and behaviors. Some people can talk a good talk, and if you are viewing that person based on their words alone, then things are great!! But there comes a point when we have to get into reality and look at a person's behavior. Sometimes reality sucks
I don't know how old you are, and maybe age doesn't have anything to do with it, but just life experience. People give off subtle and not so subtle cues about their character. Pay attention. And when you see a person's character, even though it's difficult and you want to deny it (as least for a while) don't forget it.