My boyfriend is not affectionate at all how am I so post to know he likes me if he isn't willing to show it?

This could be a sign of him not being mature enough to show his emotions / feelings to you. He might be worried about how it will look to his friends if he is so called "not manly" because he lets out some feelings. It might just take time for him to figure things out and will slowly mature. There is nothing really that you can do to move this along, it is something he will just have to figure out on his own. On the other hand he might mature but does feel as strongly about you as you do him. Either way it sounds like he doesn't want to get into a serious relationship, so be careful. Take your time and don't rush things like moving in with him. Good Luck

seems like he's scared...if affection is something you want and need in your life then you have to tell him, and if he cares enough he will make an attempt.

Maybe it's something to do with his past, or he's just not used to be being touched and loved. I'm a very affectionate and touchy person and my boyfriend was not. Not getting the loving affection back bothered me in the beginning. But when I started to spend more time with him and his family and got to know him better, I found out that he had a rough childhood. He was just not used to it. We are still together and going strong. I come from a similar background, so I understood this.
If this is why he doesn't show it, you have to teach him how. When he does something right, tell him that you liked it when he did it, and so on. he'll get better.
I hope this helped.