Would this be weird if?....?

[Some love never dies]

Ok well i will explain the situation. My mum has been dating this guy for 10/11 years and yeah well i have grown up with his kids, James & Cindy. Yeah well James has moved out for ages and he comes backs and visits us and has a couple of drinks. Well when he moved in for temporary for about 6 - 9 months this year his mates came over, and one of them asked me out on a date and he was really nice and stuff and he was like i'd take you anywhere you would want to go & i had to say no in the end because i thought it would be weird because james is like my step bro, and i have a brother and they are best friends so i just thought it would be weird. So anways, 4 months he's came over coming back on Friday and he has a really hot friend.... do you think it would be wrong for me to like crack on to him. I'm 17 almost 18 and he's 19.

Just want your thoughts & advice