What is going on in his mind?

there was a guy showing quite a bit of interest in me, looking at me, smiling, bumping into me, trying to get next to me everychance he got, laughing at goofy stuff i did and trying to make me laugh. all the cute fun stuff. i actually didnt think much about him until he began showing his interest. i asked him to hang out with some friends and he said he definately wanted to, but had to go somewhere that weekend. The next few days, were fine, one day hes suddenly not looking at me anymore, hanging out with my ex for the first time in weeks, and completely avoiding me. idk what happened. he mentioned me to a friend of his that i am good friends with: "hey i noticed you hang out with asha (me) alot..." so my guy friend told him about my interest and he said he didnt feel the same. but this was the day after he was distant...so it didnt cause it. idk what to think. im accepting he doesnt like me but i dont understand! he was so interested and now hes purposely not looking at me. is it because of my guy friend and me are pretty close and talk alot? my ex? whats the guy thinking?