One word of caution - the chances that she’s NOT having an affair are very small - not zero, but small. But the physical act is minor compared to the emotional betrayal anyway and should not be your focus.
Is there some reason you think her “infatuation” hasn’t been consummated? (Long distance old boyfriend, for example?). How old are your children? How long have you been married?
Know that you cannot control her behavior, only your own. Become the best father and partner you can. If she had legitimate complaints about you, become better. Don’t cling or beg. Did she have complaints before these last few months? She’s lost weight, so you need to catch up?
Also - how did she lose the weight? While MLC can be a factor for many, weight loss through gastric surgery can lead to addictions shifting from food to other things instead (alcohol, sex, gambling). Weight loss through amphetamine diet pills can lead to addiction.
