Best friend won't put any effort into our friendship?

[954]

We became friends not quite a year ago. & to begin would tell eachother everything, send eachother "good morning" texts, talk in the hall at school. Now, he never texts me, if he decides to talk, it's through fb. & that rarely happens, I'll send him a message, he'll read it, but won't reply. I've asked him to hangout & he agrees, but when I go make plans, he either ignores me or bails on me last minute. I've talked to him about his lack of effort & he says he'll try harder... I don't know whether I believe him or not..
What should I do?