Guys answer only please?

If she's his EX-gf then there must be a reason. Otherwise he'd still be going out with her. Have you considered that he may be bullying you into become his gf? (bear in mind I don't know him!) And, yeah a guy can like multiple girls at once. But in my experience he's got a focus on one. Best to confront him, if he does really like you than he'll admit it, if not its better to know.