When a woman reveals that her partner doesnt want sex with her she is usually bombarded with advice like "to step back and not put pressure on him
Obviously that's the wrong advice, ie where her partner wants NO sex. But where the sex life is pretty damn good by any standards, and either partner is pressuring the other for more, the advice would be somewhat different, from me any road.
As for losing weight etc, if a woman thinks that would make her feel better in herself, go for it, but she should certainly not do it for anyone else.
I read that one post on the page you linked to where you actually pretty much gave the full picture, ie you married someone knowing there wasn't a sex life, you had an affair (don't blame you), ended the affair (good move if he was a twunt) and decided not to make any major life-changing decisions, even though you could have. Life is really very much about the choices we make imo. You're 39, you could be having a great life with someone including a great sex life, but you've decided not to, like YOU have decided not to, nobody else made that decision for you.
I'm not trying to get at you, just trying to point out that the potential for change rests with you really. Listening to that program may or may not give you extra insights but really what's changed since 20 years ago when your BF clearly wasn't interested in sex? Square peg, round hole, if you'll excuse the pun.