Tread, tread, tread! Not being a MNG does not mean compromising your moral compass!
If banging some chick is something you find morally acceptable for YOU, then go ahead. Not being a MNG is more about doing what you find morally acceptable for yourself, not for what others find morally acceptable.
What you should question is how your actions are based upon everyone around you. That's not to say don't be considerate of others.
For example for me, it is not morally acceptable to use someone else for my selfish needs. Living your like to the fullest doesn't mean using other people for your wants. That would make me feel worse. Living my life to the fullest would be doing the things I desire that align with my values that don't hurt other people.
I was a Ms. Nice Girl. It wasn't because I wanted to make everyone happy for THEM. It's because I was conflict avoidant, I had no self-esteem, and I figure if I compromise myself to make others happy people won't leave me. Being a MNG is not a selfless act because your moral compass is so great.
And for the love of God, stop making your decisions on what she might be doing or the way she is living her life. You really think you would be resentful because she got to bang guys and you didn't get to bang other chicks? That's not a reason for resentment.
Do what feels RIGHT for you. And well, if your desires and your moral compass truly feel it's right to screw this woman, then do it. No one is telling you not to, it's a decision you need to make for yourself that align with your values.
