Turnedout
He's either flawed emotionally, felt trapped, and ran once it started to sound, smell and look like a relationship.
Or he wasn't as interested as he let you believe and either thought it didn't matter or it would come and then when you made a show of affection, it pushed him to end it.
Or he was seeing someone else as well, was happy to go along with it on the date so as not to get into anything uncomfortable and then ended it.
Or he's married/in a relationship and likes the affirmation of someone else liking him but then ends it when that person makes any kind of 'declaration' because he's got what he's looking for but doesn't want to complicate his situation.
Or some other, equally shit reason!
But either way, he isn't worth it and he is flawed, not you.