Jealous

In a relationship, there was a boy who keeps flirting with girls. Not actually flirting but his girlfriend can't help herself but over think so for her its kinda "flirting" I guess. She thought that his boyfriend was different from the other boys. So there's that girl named Zandria Kate, she has a boyfriend named Zak Kristoff. She knows everything about her boyfriend but her boyfriend doesn't know anything about her at all. Her boyfriend had no idea about Zandria's feelings.

Happy ending?

OR

Sad ending?