Why does my boyfriend has these atitudes? Give any advices?

He is my first boyfriend. We started to be dating but I worry that he does this sometimes I think he does it playing. At first he played with me. He pinched my stomach or touched my cheeks or played with my hair. But even before the boyfriends, he saw when some boy approached me and he changed his attitude. Playing he started touching my knee. But on one occasion a boy was passing by (who was pretending to me) and my boyfriend began to touch my neck and play with me. On another occasion, I walked over to say goodbye to him at work and I played with his hands while I was talking to a guy and my boyfriend released his hands to put them on my waist. Another time, I also said goodbye to him and there were 2 boys near him and he immediately began to caress my stomach. Once I was sitting next to him and next to him was a friend of his. I started talking with the boy but my boyfriend was in the middle, I told him to move and he did but then he started to hug me and caress my thigh while I was chatting with his friend. I was embarrassed that he did that. Why does he do this? We are already big. He's 23 and I'm 21 but I'm new to this (I've never had a boyfriend)
Why does my boyfriend has these atitudes? Give any advices?
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