Why is my ex boyfriend acting like this?

When he's sleeping with me how's this even possible ?

He tried greeting her when he was with me but she ignored him that time

How is it not??
People sleep with people all the time without even caring about the person.

Ok so therefore, she is not desperate after all.

So why do you care?
He clearly liked her when he was going out with you.
You’re well rid of him.
If she was desperate she would have been replying to him when he was in a relationship-she didn’t.
It’s not her fault he still was in love with her when he was seeing you. It’s his.
I

And introduce to families?

Yes…

OP, I'm sorry if you're not trying to be like this but why are you so against your ex boyfriend and especially his girlfriend??? They haven't done anything wrong

What yes?

You asked me a question, I answered.
Yes it is perfectly possible that he had feelings for her whilst introducing you to his family.

And his friend said he did, he tried to talk to her whilst still with you… why are you adamant that this isn’t true?

I’m sorry he used you.

It’s not her fault though.

And, he’s your ex. He can now do whatever he likes with who ever he likes.

He tried to talk but it was only cos of regret?
Because he wasn't actively seeking her out nor did he cheat on me , like trying to visit her etc.

So how he used me?

He used you because she didn’t want him when he wanted her.

Reaching out to her while he was “with you” shows that he stil had feelings there.

And Anyway- you are broken up. What does it now matter?
He has found someone else, move on.

Wait what? He didn't? He saw her in the corridors and obviously was shocked to see she was still around. Then he obviously regretted treating her badly so he just wanted to say hi?

He didn't want her cos if he did, he would actively go after her each time he saw her . He didn't.

Okay, if that’s what you need to tell yourself.

You’re not doing yourself any favours obsessing over this.
You were together, now you’re not.
He has found someone else. These things happen.

Please explain why u disagree with me

The fact she accepted him means she's desperate

I have, you just can’t be bothered to read. 🤷🏼*♀️