Why is my Cap bf so jealous?

We've been dating for about a year now & he just started being so jealous... Why?

Ugh stop it guys! This Aries has been very good!!! Lmaoooooo. I promise!
I don't know why he's getting jealous all of a sudden. What's going on in a cap mans head when he does that?

Whatever sign, everything happens for a reason. Maybe he heard something. Maybe he noticed a difference in you. Maybe misinterpreted something. Maybe he has seen a side of you in that direction and now it came to a point when he was simply fed up. I don't know. But what I do know is that there is a reason for everything and you need to find out what that is.