Recently engaged, but can't stop thinking of a crush

Hello there.
I've had a crush on a guy for five years now. We worked together for about a year and I always felt nervous around him because I found him to be cute and have a good personality. I always assumed he wouldn't ever be into me because he seems way out of my league; however, he texted me for the first time about work, then added me on Snapchat, and would send snaps with flirty captions such as "you're cute" or "you seem like such a sweetheart" or asking if I would like to hang out. Because I figured he would never like a girl like me, I didn't think he was being flirty; I assumed he was just saying silly things especially when he was intoxicated. The thing is, I've been in a relationship while this other guy was sending flirty messages. Due to that, and the fact that I didn't think he was being flirty, I would usually respond with a simple "thank you" and change the subject. However, I liked receiving such messages from him from the start. I mean, to finally be flirted with by my crush of almost five years! But I know this is unacceptable behavior while in a relationship. At first I mentioned the messages to my then-boyfriend (now fiance), but after a little while I became more secretive about hiding the fact that I was still in communication with this other man.

I know what I did was not okay, and I recognize that it was crossing the line, if not full on emotional infidelity.

My now fiance and I took a brief break/break up, and when we got back together, he proposed shortly after. I was happy and accepted, but I can't stop thinking of the guy I still have a crush on. I feel terribly guilty. I don't communicate with him anymore, but only because my fiance made me unfriend him on Snapchat. I was intoxicated recently and became incredibly sad, and the first person I wanted to talk to was my crush; I tried to add him back on Snapchat to talk to him, but thankfully I was too drunk to find him on Snapchat. I've reached out to him via Snapchat before when I was drunk and sad.

What are your thoughts about the situation and what I should do? Do you think I have simply idealized my crush in all these years of crushing on him? I mean, I don't even know him well. How can I stop thinking about him, and wanting to turn to him when drunk and feeling sad?

I apologize for the long explanation. Thanks for any input!

This. You can't help who you fancy, but you can control what you do with it.

Also, Sod's Law says that you'll like your crush all the more for knowing you shouldn't do anything. I imagine that's happened to us all.