Suffice it to say that I, through my lack of initiative for sex, turned my marriage into a roommate relationship. My wife could not stand this after 16 years (and I, in many ways, cannot blame her), and decided to lose a bunch of weight, do self-improvement and go looking for someone to pay attention to her.
When women start losing weight and trying to look good, they have already decided to find and attract a more worthy male. I'm going out a limb (not much of one) and guess that she lost weight and you kept getting fatter. Which brings us to the root of the problem which she used as a pretext for her adultery: your disinterest in plowing her good and proper on a daily basis. The fatter the male gets, the more estrogen and the less testosterone he produces. The higher the estrogen in the male, the fatter he gets. It's a closed feedback loop that's turning you into a girl-repellant eunuch, for all practical purposes.
Did you get that? Not only do you not want to have sex with a woman, they don't want to have sex with you. Once you get your waist/chest ratio out of whack, you become invisible to women. Been there, done that.
Go on Atkins induction and stay there until you get a 32" waist. Simultaneously, take up bodybuilding. See your doctor about a T panel workup, you're clearly deficient. You want it around 700-800. Cool how I can diagnose that over the internet, ain't it?
Take advantage of your wife's absence while she is on her sex tour to haul off the crap in the garage. Better yet, have a garage sale and make some lawyer retainer money.
If you want to get your wife back, that's a tall order. She checked out the first time she said no to a hot fudge sundae. Your only chance is to whip your body into shape ASAP and learn how to get in touch with her limbic brain. Read Roissy and Married Man Sex Life. The lessons learned will be useless, though, unless you fix your hormonal and physical deficiencies first.