You do know that a good guy can care and love a girl because of her personality. Its not all about looks, honestly id say looks are 40% of attraction, obviously when you first meet someone then looks are 100% but after you meet and get to know them it goes down to 40% imo. He likes and cares about you and is happy to be with you. So quit doubting him and embrace that a guy comes along who doesn't only care about looks, there isn't that many of us out there :)
U might think tht you have average look but he might think different.I personally think tht for him you are pretty or cute(if not y is he with you now).He also might likes you because of other reason.Maybe you have the greatest personality among all the girls he ever met and tht really catched his attention.We can fall in love with someone not only because of their look but also because of something special tht they have;)
He probably isn't going on solely looks. You have a personality he likes. I'm not saying your ugly either (I have no clue what you look like) but just saying, there is more behind it than just looks. Be happy! He likes you for you!