I think you are falling for an even older line.
The line that says you "fell". The line that blames the "story".
You didn't fall. You chose to walk across a line. No tripping, no stumble required.
His "story" included an ongoing relationship that required your liaison with him to be a secret. Regardless of the other details he included that may, or may not be true, you were aware of her being the collateral damage of indulging your own desires and decided that helping to bomb her life was fine by you.
I don't think you'll get out from under him and this scenario until you stop making excuses for yourself, quit wanting to put all the blame of "us two" on him and taking responsibility for own own actions and choices. Nobody has control over your central nervous system other than you.
This was not something done to you. It was something you decided to involve yourself in, for your own reasons, regardless of the cost to anybody else. While him lying to you is wrong, he told you enough truth for you to be well aware that your own moral fibre was always going to be too glass house flavoured to be chucking stones all over the shop when the "bit on the side" status quo no longer suited you.
Pick the kind of person you want to be, act like that person, fake it till you make it if needs be and life will improve. Or keep blaming everybody else for your choices and live longer term with the lack of happy you are currently experiencing.
It's your life, you get decide what you want it to look and feel like. Just like you have so far.