Is he just immature or have his feelings for me changed?

He's probably just a little sour over the whole why doesn't she tell me she loves me thing. He's probably the type who falls in love fast. Be careful, those types fall out of love just as fast. Give it some time, be a little more affectionate, but only if it is truly how you feel. Be yourself and take it slow. If he really does love you, he'll stick around. Good Luck!