10th anniversary coming up, but deep in an affair

Hi there - I'm new to this forum. I signed up to this forum because I simply can't talk to anyone in my family or among my friends. I really hope that I can talk to someone here. Feeling desperate.
Let me try to keep my first post as succinct as I can. I love my partner very much; we'll be celebrating our 10th anniversary in a few weeks. His work has taken him abroad - yes, I can hear you going 'ahh' - and suddenly I have a few months on my own. A colleague of mine, whom I've known for a couple of years and speak to on occasion whenever we bump into each other (we're from different departments), asked to review a project with me a while ago (we were put in the same group because of work). He's an attractive man who speaks well. Working late with him led to sharing drinks and kisses. I knew he was going through a tough divorce, and I felt bad and immediately apologised and said we should stop. Somehow, none of us stopped and we became secret lovers. We're falling in love, and are exchanging texts when apart from each other. Everything that I do and share with the new man reminds me of my early months with my current partner. It's all too overwhelming.
I'm feeling awful - everyday I speak with my partner, almost every night I kiss the other man, and every night I beat myself up before I struggle to drift off to sleep.
What's even crazier is that last night I made a list for both men. They're both very good-looking, both great kissers, both great in bed, both with jobs that one can be proud of. I hated myself for having made the list, but the pluses on the other man's side are glaring at me.
10 years vs 2 months... but the intensity is oh so strong. I'm on the verge of breakdown - can't focus on much. I used to wake up to the thoughts of my partner and go to sleep saying goodnight to my partner, but now the new man has displaced my partner from my thoughts...
What's happening to me? My rational side says 'stop it', but the rest of my being is all consumed by emotions for the new man.
I hate myself.