Help guy advice?

well this i guy that i thought was still my best friend all of a sudden goes from talking to me all the time to just not answering me literally the next day, well we used to have a thing but i didnt want to date so we both decided on friendship and i thought it was going fine but than he decided im gunna ask out a girl i hardly know and wanna know who he asked for advice ? me.i was kinda upset cuz i stll care about him but i didnt tell him that bc than itd make a big mess of things, so i would just ask about his date with the other girl an he kinda got surprised i guess cuz he didnt think i would say anything. so hes been dating her for like 2 days ,well obviously im kinda jealous but mostly mad bc a day ago he goes from asking to hang out just the other day and saying dnt worry just cuz i have a gf dosnt mean were not gonna hang enymore to next minute where he just stops answering my ims, dosnt say anything to me..so idk what hes doing n i need opinions please if enyone can help.