I can actually relate to you in a few ways. First, as a married guy who identifies as primarily heterosexual, I have still had several m2m hook-ups over the course of the years. These are not necessarily something I'm proud of on the one hand, because they are not in keeping with the promises I made to my wife and family. On the other hand, I can't seem to stop, and, at times, don't want to. When I traveled more for business, I would hook-up when I could on the road. Now that I don't travel much, I've made a few fuckbuds locally that I visit when we can work out the schedule.
However, I think you're letting your guilt over the sex, and, frankly, your clear enjoyment of not just the sex but the connection you and your co-worker make when you do have sex, cloud your professional judgement some. You say you are a "go-to" guy for people, and your bud may see you the same way, which would help explain his e-mail from a professional perspective. So be cautious of reading into it more than is there.
His avoidance of the issue despite your hints isn't all that hard to figure out, really. He may not have been in a place he could talk about it, or he might be in major denial. If you really want to know if your hook-ups are playing a part in the consideration of the move, then ask him straight out. I think you may be hesitant to do this because you don't know what you'd do if he said "Yes, they are, and I'd enjoy being closer to you." You are, in a word, conflicted.
I would relax, and then be honest with the wife. Since you don't have kids and you aren't being honest now, you'd probably feel better if you told her that you liked men, too, and are feeling torn and dishonest about that. At least if you divorce, you'll be on clear terms. If she knows you row both ways, and yet still wants to be married, then maybe you have something to build on. Isn't it the infidelity (regardless of the gender with whom you cheat) that makes the relationship unstable? Be honest with her and yourself.
As for the potential fbud in town, and potential competition for the same job, I think you need to be honest with Miguel, too. Tell him you think he's sexy and that you feel a connection that is hot as hell when you're together, BUT you don't know what to do with that. Then, let him tell you what he's thinking and feeling.
In short, be honest with yourself, your wife, and your fuckbuddy. Then re-evaluate.