Why am I so jealous?

Constaince • Trying to convince. Sex is hard work
I hate that I'm so jealous! My fiance will look at a video of something and it has a half naked chic in it. I know that sounds so stupid, I think it does. He lies about it is why I get so upset. I mean it's not porn! Why am I like this? I want to stop being so jealous but it's hard. Why is something like this I want to change so difficult.