Mixed feelings about a relationship that ended 3 years ago?

[Emi]

I was logged into Facebook on a friends account, i went to go log out of it since i respected her privacy but on my dashboard was this picture of a guy, his eyes reminded me of my ex boyfriend.
I made the wary decision to check on him.. because i was curious. His Facebook profile popped up and his picture was on my screen. I smiled, a lot which surprised me. This guy was my first love and strongest love, we dated for 4 years, and we broke up 3 years ago and haven't spoken since.. we ended on bad terms. I was pretty content that i've fallen out of love with him since.. but i smiled when i saw him, and after about 10 seconds of smiling i had a huge rush of feelings overwhelm me and i just broke down crying, i don't get it. What do you think?