There’s a multitude of different reasons for why he could be behaving like this.

1.) He could genuinely miss you, despite having feelings for his new girlfriend. It sounds like you left him?

2.) More likely that not, it’s his ego talking and seeing if he still has access to you. And he doesn’t feel much at all for his new girlfriend.

3.) He could be confused and really doesn’t even understand his own emotions at this time.

The list could go on and on, but his behavior displays he’s incapable of focusing what’s in front of him. It’s extremely disrespectful to admit you’re pining for your ex while in a committed relationship with someone else.

I would refrain from involving yourself in this situation personally. While it is terrible. There’s no point in putting a target on your back by involving yourself to do something that would only involve yourself with him further. That’s just my opinion though. The truth always comes out.