Boy problems... please help

I know my ex still likes me, I still like him too, but he has a gf and I'd never try to ruin someones relationship. He tells me daily he cares about me and wants to date me and he's told me in the past he has no feelings for the girl he's with. Today he and his gf were right beside me and he kissed her, looked at me to see if I saw, then kissed her again... it's really irritating and it hurts me, but I don't know what to do...