Sorry to say, but the manual was the book from which your wedding vows were taken. Were ya listening? You have three children who will now be affected by your midlife excursion and you are going to change who they will become because you weren't getting any sex and your wife was over-weight...sheesh. Why'd you have three kids?? Wasn't she over weight after the first one? Oh she was still trying to please you at that point I suppose. So now you are going to totally disregard your wife and daughters futures so you can get laid by an old flame.....that is terrible of you, you should be ashamed of yourself.
You need to do everything you can to save your marriage and your family. You need to stop blaming your wife for everything and take a good long look in the mirror. You need to end the affair and commit to never contacting her again. (You don't say much about her...is there another marriage being destroyed and more kid's lives being ruined??)
I'm not going to be popular for this response and I don't care. You need to GROW UP and stop thinking with your d**k.....you ARE going to be alone when you are old if you stay on this path.