I am a former OW myself (as well as a BS before that).
I will tell you that I felt similarly for a while about never being able to get over the attached man I was with. And I could definitely see myself still feeling that way still if I hadn’t sought help after the affair ended. I was terrified for a while to be with anyone else, because I was worried that I’d still be clinging to feelings for him because it was “true love”.
Affairs bring about strong feelings, not because they’re based on true love, but because they’re based in deception and lies. When you’re with someone who is in a committed partnership with someone else, you feel “chosen” in a way, this person is putting everything on the line for you, risking their entire life for you. It’s an intoxicating feeling, but it’s not true love.
Ask yourself this (because I also had to ask myself the same things): Do you truly believe your “true love” would have to hurt another person to be with you? Do you truly believe that if it was “true love” that this MM would still, years later, be unable to be with just you? Does “true love” need to be hidden? What has your MM actually done to show you he loves you? I think you’ll find if you look at the situation objectively, it’s not much more than words.
I think you would find, like others that have been in our shoes, that if the day did come that you guys were in a real relationship, things would soon fizzle out. A LOT of the intense emotions that come from being the OW come from being “chosen” over the primary partner. If you ever become the primary partner, your focus will likely switch, things won’t be the same. And even if you can be happy together, you’ll always know that your happiness came at the expense of another person, a person that was by all reasonable expectations, totally innocent and undeserving of that kind of pain.
I would suggest looking into independent therapy sessions. Most Other People (myself included) need to take a deep look at themselves and figure out WHY they were willing to settle for what little their affair partner was offering. WHY they could turn a blind eye to someone else’s pain.
Your issues in your current marriage could be valid, and I wouldn’t so quickly dismiss them, it’s also worth maybe looking at your happiness, and your spouses happiness and seeing what (if anything) you can do to be happy and fulfilled. I also think it’s important to be honest with your husband about what’s taken place with the MM during your own marriage, if you haven’t already.
I will say this, I spent months in therapy and I’m doing quite well now, at least on a personal level. The attached man I was with before rarely crosses my mind anymore, except when I’m here, which is why I’ve been limiting my time recently. I met someone else, and I can honestly say that I don’t find myself comparing the two relationships. I have learned to forgive myself, and I’ve moved on. I hope you’re able to do the same.