When my marriage ended I did see some of it was my fault / we rowed every day.
When I remarried and saw my self acting in the same way and I new I had to change or this marriage would go the same way.
No one is perfect.
Marriage is hard work and needs work.
An affair is never the answer.
But if someone accuses you of being Cold I'd be looking at that. My ex dh was cold and it is another reason we split.
Also as pp have this ow was a fantasy.
Most married men do not leave their wives for ow and those that do quickly realise the grass is not greener.
I do not think you are second best. You are not. He did not leave you for her. Even thought he maybe looking back with rose coloured glasses at the fantasy.
He fucked up, and though you have every right to angry , to throw the affair in his face will not lead to healing for either of you.
You need to bill yourself up to be the strong resilient woman I know you are.
I agree with @SandyY2K about get on with your life.
Then you can decide what you want on your terms.
Good luck.