HEEELLLPP!!! Ex-Boyfriend acting weird...?

[TrinaTila]

My-ex boyfriend is 23 and Im 18, we dated for about a month and 2 weeks then broke up. It's been 3 weeks since we've seen each other. And he said he wanted to be friends, and I said I would try. Then he mentioned being FWB's, but I said no. And he said okay will just be friends. So We were supposed to hang out on Thursday and I asked him if while were out if it was okay if he could buy me alcohol and he said "no, I dont wanna" I asked why and he said "I just dont want to", I made a joke saying "You suck, No Fun" and he said "Yea whatever". Later I asked him if he was mad and he kept saying "I dont care" "I could care less, dont worry" "I forgot all about it". and hes being mean to me. I didnt do anything wrong, he wanted to be friends so thats what I'm trying to do. I'm just so confused. I mean sometimes I make remarks about other cute guys on twitter, but I'm not seeing anyone. Why is he so mean to me all of a sudden.