Oh,
@Daniel A, I feel for you. You are stuck between and rock and a hard place. Your conscience AFTER YOU BLEW HIM (your brain head) is now at odds with your conscience BEFORE YOUR BLEW HIM (your dick head).
It's called remorse. You got a big case of it. I would advise you in the future to think with your brain head BEFORE you do anything sexual with anyone, especially in a work environment.
You've gotten some excellent feedback from many posters above. It's spot on. Don't fuck around at work. RARELY does anything good come from it. Before you do anything at work, you need to think: What's the worst that could happen if someone finds out about this? Like losing your job? And if you can accept that, then blow on.
In no way am I absolving your manager of his culpability. In fact, I think he's the poster child for sleezy stupidity. And don't get me started on how his partner may be affected should he become aware. It's just a fucked up scenario you've described. IF I were the partner and learned of this tryst you describe, your manager would be looking for a place to live. Immediately.
I managed people for 22 years. Yes, there were inter-office romances; when they went sour, and they almost always did, it was not pretty. There was always collateral damage. Innocent family members suffered. From the divorce. From the loss of the philander's job.
I'll never understand some people. So many oceans from which to fish, yet you each went after the easy catch in the small pond. Cuz it takes two for a successful blow job, right? Unless one is quite flexible, lol.
Regardless, the horse has left the barn. Make sure this was a one-off. One and done. Don't shit where you eat. Think with the head above your neck next time.
There is a personal characteristic that I greatly admire in those who have it, but which is lacking in so many. It's called self-control. You need to learn that skill.