I don't see the win opting for a separation & divorce w/ a 9yr old daughter in the balance, just so I can date again and be emotionally & physically intimate with another woman. Its possible I'd make the "once she's off at college" argument in 10 years but thats pretty major future-tripping so not worth the time spent thinking of it.
My ES&H. I do not have children but am the daughter of parents who should have divorced. Now they are old and sick. My dad is 80, my mom is 77.
I can't tell you how sad it is that at end life the one thing they chose to do wrong was stay married, and deny themselves happiness elsewhere be it with someone else or alone. I am convinced that near 100% of their marriage is the reason why they are both sick - its the stress. Denying yourself physical intimacy is stressful, denying yourself a healthy relationship is stressful, denying yourself companionship as opposed to accepting blunted "putting up with each other" is stressful, and then the periods of "black cloud" situations when it would all come to a peak and explode. There is nothing shameful, or wrong, about wanting something more with someone else, it doesn't reflect on your parenting Mine will say sometimes they wish they had never met, and they had a great marriage for about 15 years. They do love each other, they do have common interests, they do get along about 50% of the time.
Yet they also hate each other too, resent each other, blame each other, the other 50% of the time. I don't look back EVER and say to myself "Oh I am so glad mom and dad stayed together so we are not a product of divorce". It makes me sad they stayed married. Very sad. And there have been great and wonderful times - and we have pictures of my parents holding hands, kissing each other, great trips as a family, great times as a family. So what? It came at a large price for those Kodak moments - their happiness and a hardship on their kids.
I think the longer you stay in a relationship the harder it is to get out. I begged my dad to divorce when I was 18, wasn't a good time because we were in college. Then at 25 it wasn't a good time because we were all getting married. Then at 30 the grandkids were coming and it wasn't a good time. It was never a good time.
10 years is a lot of life to give up, imagine 56 year. Blink of an eye.
I think its admirable that you care so much about your child as to make that sacrifice, but there is a flip side that affects the child very negatively in the choice to stay in an unhappy marriage.