Why would he want to do this to me?

So yesterday, my friend told me that my leo ex wanted to talk to me and he needed my number. She said she will ask and if I give her permission, she will give it to him. Later on she found out the reason he wanted to speak to me was because he wanted to get back at his girl for cheating on him. Why is this happening to me? I was with him for two years, he was my first love....why would he want to treat a good girl like me that way?

It's not a Leo thing. It's a douchebag thing.

He may not be intentionally set out to hurt you at all. It sounds to me like he may be too self-absorbed right now; consumed by his own anger and resentment to even realize that he's causing you any pain at all. He's seeing red and is blind to all else. So don't even give him a second thought. Blow him off and don't be an enabler. He'll either find someone else he can go create drama with or, if he's a true Leo, he'll come back to his senses quickly. Our tempers are easy to rise but they fall just as fast.

Us leos can be selfish. We do not deal with pain of any kind that well. So we become (as has been said) so self absorbed we forget about what happens around us. He will realize latter what his actions does to others. It will depend on how mature he is rather he will acknowledge it or not.