Why do guys act interested and then disappear?
There is some detail to be taken into account: how many dates did you have with him, how long was the relationship, were you his “official” girlfriend?
If you only had 1-4 dates he owes you nothing. No explanation, no nothing. He may disappear whenever he wishes (and you too!)
If you had more than 4 dates but you are not his girlfriend, then a simple phone call is enough. Also, it depends on how you turned him off — if you behaved like an annoying idiot, humiliated him, etc — he may be in his right to disappear from your life without any explanation even in this case
If you are his girlfriend, then he owes you a face-to-face meeting. He should give you a bogus reason to make you feel less crappy (like women do) “it’s not you it’s me; you’re too good for me” — this kind of bullshit women are experts at. He still doesn’t owe you any explanation or impressions. When it’s over, it’s over.
Now, for the why: he lost interest in you — you turned him off somehow. Contrary to what your “comforting sistas” will push into your head, it’s about you. You turned him off.