My ex boyfriend keeps staring and smiled and said hi what does it mean?

He might just be.. sexually deprived? So he is temporarily forgetting that he "can't forgive you". I could be wrong, but it is probably something to that effect.

I'm a virgin and waiting until marriage and he knows that

Don't underestimate the power of horny..

okay.... for weeks on end, being horny and getting flustered have nothing to do with eachother

Guys, typically get over grievances easy. Maybe he has rethought his statement. Maybe he can justify what happened. You both were upset and said off the cuff things. Maybe when he sees you, he can't hold a grudge because he wants to be your first. I don't know. Trying to rationalize things like this is nearly impossible without taking into consideration all the factors involved. Trying to understand the opposite sex is more complicated than rocket science. Many aspects seem to make no sense at all. Or it is easily contradictory. Humans are rarely if ever consistent.

I think the whole thing should be approached from a different angle. Ask yourself if you think he is too immature to date because he likes to insult your mother. If he is willing to do that, what prevents him from doing it again? Are you willing to look past it all? If you aren't willing to look past it all then you are better off forgetting about him. But if you can deal with it and you think he is worth a second shot then by all means try it. But trying to understand why it all means, is nearly impossible.

So let me see if I get this right - you hadn't any interaction for 2 months and before that there was a 2 month space.

If you still want to be with him, go for it. Ask him is there ever a chance or is it totally over. Take it from there. If he refuses to answer or says it is over and he will never forgive your insult of his mother, turn around and get on with your life.

why do you think he's acting like this though? Not acting like someone who isn't forgiving

You will have to ask him.