How do I know if he likes me?

Ok there is a couple of things that may be going on here and time is the answer. He may like you or he may be trying to get his ex to realize what she has lost and make her jelous. Think to yourself did she have a problem with you? If so, he knows this will get to her. Just give it time and keep on doing what you are doing. If he wants more it will come out but, stear clear until the ex is completely out of the picture.

Talk to him about it. Ask him if he likes you, and tell him that's the vibe you're getting from his actions.

Ask him what's the deal and if he likes you just be honest and don't act like someone you are not if he does like you.

Give it time! He may still have feelings for his ex. unless you know this is not so. But from the sound of it he may be interested in you. But just take it slow and give him time. When the time feels right then you can talk to him about it. Then just go from there.