Im glad you noticed that NGS is a huge resentment builder and marriage killer. Of course I read NMMG after my WW left me and I realize it now but I guess better late than never.
You will find a lot of LH19's stuff follows along what Corey Wayne would say on youtube, he has a very agressive take it or leave it approach, but something he says is totally worth putting in your pocket especially regarding NGS and it is "A relationship is about giving, you go there to give and not to see what you get in return"
Good job connecting the NGS and resentment its big.
The nice guy stuff has been a bitter pill to swallow but damn I wish I had gotten to it sooner. Of course, even if I had chances are I wouldn't put them into action out of fear of rocking the boat. I do now have a better sense of assertiveness and confidence. I don't know if it is real or wishful thinking but either way - fake it 'til you make it!