Shifted from her friend’s problems to comparing their respective sex lives to this man’s assets.
Her response was immediate and enthusiastic, and with THAT shift, your wife went private mode. This friend doesn’t need your wife to workout or diet. Ditto for speedily delivered lingerie.
Given her motive, exuberance, secretive discussion and preparations — plus opportunity, which makes more sense to you:
A] A weight loss narrative.
B] He is porking your wife.
So — what way forward?
In your place, I’d work on creating an environment where it is safe for her to discuss her issues.
You could confide to her that YOU know her love life is running seriously substandard, and that she has to know this herself, and that it is so blatantly unfair that she is missing so much of the best of life because of YOUR shortcomings.
Explain that you love her dearly and would agree to anything to fix this. Tell her that this has plated on your mind for 3-4 years [since you’ve been having problems] but that you felt helpless to fix it since — well … your body is what it is…’
Tell her that you feel so guilty that she must do without because you ARE without [much]. Tell her that your inability to face and discuss this ‘even with my own wife’ shames you to disgrace. Tell her that it makes you feel unmanly. Tell her that you’ve realized that you can’t move forward or mature in respect for YOURSELF—UNLESS you face this fear, and that to face this fear, you have to be brutally honest with yourself.
You can say that you learned that when she uses humiliation with hand-jobs. Tell her ‘that works because it’s true.’ Ask her, ‘how can I love my wife as the prophet Mohammed peace be upon him taught IF I can’t even be honest with her.’
For many wives, your issues would be an outrage. Tell her that ‘I can’t in good conscience see her denied any longer of what is her’s by right.
Tell her that she’s given her girlfriend plenty of support. Ask her if she has any thoughts on how to resolve these things, and that you’d be grateful for anything she says.