What are the possible reasons behind a guy ignoring you?

Maybe he just wants some space from himself and does not even realize he is ignoring you.

He wants personal space

If you guys used to be close and suddenly he has stopped all communications, there is a high chance that he is going through something, or there is some problem, but he cannot share those with you.

He is not good at communicating

Maybe he is not finding you interesting or has changed his mind about you.

He doesn’t want to be around you

If he likes you and knows that you like him back, he might start to ignore you because he fears commitment.

He has commitment issues