Why do i feel this way, about a guy that's way older than me??? help!!!?

I'm 15 and my grandmother owns this thrift store so she picked me up from school one day, on our way to the thrift store she was telling me about this young guy that just volentereed to help one of her employies that stalled out and she was calling him an angle and making a big deal about him so i just kinda over rode it then i was at the computer at her store and i saw this guy and he looked to me like he was 18, 19, 20 but i was hoping he was 18 lol cus I like NEVER think a guy is really cute but he was lie the cutest guy i EVER saw idk maybe im just carzy or something. He stopped and the workers were trying to get this big trunk thing off a truck in the store and he came and just carried it in and sat it down so my grandmother called him over to her register/counter and was telling him he was an angel and all this stuff, he kept looking over at me and i was thinking hes SOOOOOO cute/hot, soo about two months ped and he kept coming in and ever since i saw him i had dreams, fantasys, thoughts... etc about him i ust couldnt stop he is like the cutest guy i have evr seen, come to find out he has three kids that are form 2-6 and even tho i found that out i CANT stop thining about him. I finally started to and today there this older guy im close to (meaning i can talk openly with him) and we were talking and i brought up "do i look older than 15?" and he said yeah... then he told me "you know that guy your grandmother calls her angel" and i said "yes" then he said "well he thought you were old cus he asked how old u were cus see he likes u and he thought u were over 18 and i told him U werent" evr since that ive been having these like weird emotions and i kow this sounds SO dumb but i just have these dreams when i fall asleep about HIM and i think about kissing him and me being smaller than him and all this stuff I CANT stop thinking about... Plzzzzz help me!!!