Affair after Weight Loss

Basically I think it boils down to this:
We can be idealists and talk about how it's wrong all we want, and it IS wrong. Unfortunately though, it still happens, a lot. but I've seen countless situations where relationships fall apart after one partner loses weight. You have multiple situations:

-One loved the other when they were overweight and meek. They was disturbed and threatened by a new-found confidence and went looking for another partner either to hurt them back or to replace their old role.

-One partner loses weight and suddenly gets tons of attention from attractive people. They give in to temptation.

-After losing weight a person feels that they've undergone a very spiritual transformation as well as physical, and feels a need to sever themselves completely from their old lifestyle, including friendships or relationships. They can also feel like they aren't connected with their partner anymore.

-One person becomes so excited about fitness that it consumes all of their previous hobbies and interests. They now want to spend their weekends at the gym or on long hiking trips, and the partner doesn't want to tag along. They simply drift apart or gradually become interested in someone else whose hobby is fitness.

-One lost a significant amount of weight and would never admit it- but all the vanity went to their head and they suddenly found themselves "too good" for their old partner.

-One partner changed, the other didn't, and the same way the thought of eating an entire gallon of Ben and Jerry's grosses someone out after getting really fit and breaking their junk food addictions, watching someone else continue in that lifestyle with no guilt, remorse, or need to change, just simply grosses them out. I've seen this happen multiple times- even though a person used to have the exact same habits, somehow witnessing their partners continue on that road repulses them (and maybe reminds them how they used to be.)

-The relationship was never a good one and one side loses weight and gets the guts to finally get out, and uses an affair as the spring board. (As bad as it is, I've seen women use affairs to get out of a bad or controlling relationship by hurting the old partner so he wouldn't want her back.)

-One partner lost weight and there was an imbalance of sexual attraction after that. In my opinion, when this happens, the sexual relationship of the couple was doomed from the start and wasn't based in love and intimacy.

Now that I've written down those situations- I realize they're almost all valid reasons for ending the relationship. They are NOT however, excuses or acceptable reasons to cheat. There is never a reason to cheat. It's the honest truth though, that many of the above situations are accompanied by or spurred along by the budding of another relationship. (IE, a person's been wanting out the relationship for a while for one of said above reasons but hasn't found the confidence yet, but after meeting someone they're interested in they suddenly get motivated to ditch person A for person B.)

If you're feeling like you've moved on or transformed in more ways than just the physical, and you realize that your relationship is at odds with your new lifestyle, I encourage you to talk to your partner. Decide if the relationship is worth fixing. Decide if the above situation was from the shock of the weight loss, or is a lasting and serious change. Realize that many things can be worked through, but if you find yourself gravitating toward a new person or a new life, for the love of god end the old one before hurting your partner.