I literally can't stop thinking about him

Some background story to make it shorter in the end: My sister got pregnant by accident. Our mother knew before my sister knew herself. It was during the holidays that my mom wanted to get rid of my sister and moved her in with my brother. At that time, however, my brother had moved out of the apartment. My sister took a liking to the man in the apartment, and they became a couple. Unfortunately, the baby died shortly after birth, so my sister has been feeling a bit strange lately. When I told my mom about it, my mom told my sister to get away from the situation and offered my brother's apartment. My brother is currently abroad, so the apartment would be free for some time. My brother also agreed and said that he would stay elsewhere when he returns. But I had a hard time dealing with the situation. I'm 20 and he's 25. Meanwhile, I actually always got along with my brother, but I used to live in my mother's house, while he lived with my father. He always helped me out when I needed something, so I never thought of him as a hook-up. But now I just can't keep my hands off him! The other day, he offered to pick me up from work, and the way he smiled at me from behind his sunglasses made me melt. I don't know how I would feel if something were to happen between us. Or should I say: how I would feel if something didn't happen between us.