In love with someone else

Before I got with my SO. I was dealing with this guy for a few yrs on & off. I had the best sex in my life with him & love how he made me feel on dates or even just being alone with him. He reached out me recently and basically said he feels the same way I do. I think about him all day everyday... Even when I'm having sex with my SO. I think I only got with my SO BECAUSE I WAS DESPERATE & lonely