I do sympathise (and empathise) with your own feelings and how you view yourself Grand, it's just that I can't see any way at all that being the OW will 'fix' anything.
Quite the contrary, it will just make it worse & perpetuate it.
In the case of my ex, he'd been seeing the OW for 10 yrs in total (I was entirely clueless); it was much the same as you, whereby it was an infrequent physical thing but a continual emotional contact (emails, phone calls etc). I think the entire totalled time they physically spent together over the 10 years was probably about 2 months (if even that) - it was snatched shags here & there and practically no actual 'relationship' (as I would view a relationship - going out together, shared experiences, holidays, meeting each other's family etc).
When I found out I left him - he spent months trying to get back with me, he dumped her immediately I found out. When it became clear I was not interested he hooked back up with her & they're still 'together' now - but she's still his 'dirty secret' to all intents & purposes.
She's never met his family, or our kids; they still have only sporadic physical time together because he prioritises the kids over her, and he spends more time in my company than hers tbh (we're amicably co-parenting).
He doesn't respect her, he ditches her plans at the drop of a hat & he sees her as convenient. I would not be surprised if he ditches her if a better offer came along tbh - he's made it clear to me that if I would get back with him, he'd finish with her.
So, what I am trying to say is that you deserve more. Much more.
(As does the OW in my case, but as it was me & my life that she colluded in destroying I actually couldn't give a fuck about her or her happiness tbh).
You don't need a partner to validate or define you, you are so much more than whoever it is that you happen to be shagging.
It's fine to not be in a relationship - what do you get out of the relationship? Where else could you find that?
I like myself, I respect myself, and I absolutely would expect the same from any future prospective partner.
That is how it should be, and we all deserve that as a minimum, you included. 