Personally, I'm saying that there's nothing there that tells me she had an affair.
She did what any woman would do after losing lots of weight and getting in shape. MMS hit the nail on the head when saying that when you lose a lot of weight, it does wonders for a person, especially sexually.
Everything she did was normal for someone who lost weight and is feeling so much better about themselves and I'm not gonna get this poor guys blood boiling over something as serious as having an affair, with just what he told us.
Unless he has something else to add to the story, I don't see anything out of the ordinary here.
Maybe now that she's lost all that weight and looks great, it made him insecure and is worried about losing her. Him having had his health problems could easily have made him feel insecure.
Now she lost all the weight and feels sexually attractive enough to be much more comfortable in bed doesn't mean she had an affair at all. I've been fat and thin, so I can say I've been there, so it's normal, but if he treats her like someone who did something wrong, then it's a wonder why she put away the sexy cloths