This is actually two questions...

1. You need to be secure in yourself to be jealous. Even if someone has something you clearly do not... it's not about trying to take things from other people. But instead figuring out how to better yourself. Kind of a change in perspective.

2. Constantly teasing and making jokes with you, touching you or close-to touching you, lots of eye contact, smiles, and 'open' body language and relaxed posture.

Tough to get over feelings of jealousy as it is an emotion. When a guy flirts with you, I believe that you will know it. Look for eye contact, what is said to you and how it is said. Actually, flirting can be non verbal. A glance, a smile, et cetera... 😊

I don't know first one but if a guy starts conversation with "how you doing?" Then he's flirting ;)