What does it mean when a guy flirts with you and a lot of other girls, and he is also your ex-boyfriend.

Why is he your ex-boyfriend? What happened with that breakup?

That will help provide some more insight to his behavior.

We're in high school, and didn't talk a lot, and didn't talk at all when summer came.

That's probably his nature. He sounds like the popular friendly type. Don't be jealous.