Is it normal to date step-brother?

This is going to sound like one of those fake stories but it's not.

I met my now step brother before I knew my Mother was interested in his Father. I live in a small town and he worked at a game store. My [blood] brother is a game addict so he constantly wants me to drive him to the game shop to get some new games/exchange whatever. One of the guys who works there is drop dead gorgeous and I am super into him. I've talked to him while my kid brother who is 12 was looking at the games and although we only talked a little bit, I feel like he could be interested. He smiled, laughed, acknowledged me when I came in every other week..

Fast forward and my Mother tells me she's been seeing a guy who runs one of the cafes in town. I tell her that's awesome, I meet him and he's nice, her type. They dated for a while all while I still crushed on the guy at the game store. Maybe three months passed that I knew him until she said she wanted me to meet his son..

It was him..I was in shock. He was in shock... but then he stopped working at the game store and he only visited our house once after the last time.. and he didn't talk to me or try to contact me and went back to his last yr of college which is a few states away. I missed him the entire time and thought about him. He came back a few weeks ago and he has only said hi to me and won't look me in the eye or ask me anything.. my mother and his father tied the knot at a courthouse last weekend.

IIN? I want to date him and that he's avoiding me? He doesn't even give me his phone number yet I have his father's number.. I really like him and I feel he probably feels the same but is this okay to even do if it's a step sibling? :(