I don't think anyone believes you were caping for him.
Real shit. I was the side and so far it worked for 6 years going on 7 years. We were fucking around for 4 or 5 years before this. In fact, as i type this, I'm not going to disrespect myself by saying i was a side. Mistress or whatever the male equivalent is more respectable.
Im not a traditional relationship type of man though, so my mindset is partly why it overall works for us.
Clearly, im not a person who believes you can't wife a side. You just may not have met a person under the best circumstances. The reality is alot of people cheat and most people breakup. It may be low probability but leaving for your side could work. If it fails, it's no different than most relationships that failed end of the day.
I agree relationships that start from this aren't likely to succeed. One you both remember the person's behavior so anything they do you relate it to when they were cheating with you. You probably never trusted each other to begin with. Then, you may have never meet the real person. There was no investment before, so most of your times were good. The good times with your side actually did damage to your relationship because of the illusion of a better partner.if you had kids or other responsibilities, you temporarily left them behind which helps with the illusion. If you actually leave your wife, nothing changes and it could be worse because you never really knew the side. Some people literally get off on the thrill of cheating, so when you are in an actual relationship with the person, the person loses interest.
For it to work, the person can't just be filling some void (sex , communication) your wife didn't fill. You really do need to work on yourself and know who you are dealing with. Otherwise the problems just carry over to the new relationship.