Only boyfriend EVER. I'm 23. Jealousy, Betrayal...etc?

Ok. So I started dating this guy and did for 2 years then he broke up with me, a year later we reunite, but he had with his "in between" gfrd. We were each other's first. Im practically tortured by thoughts of her and I feel like an immature idiot. Sometimes I feel like I am not that attracted to him anymore, but I love him and want to marry him. I feel like a middle schooler.