You give two Options, A Affair, and B Divorce. I choose C Laying it all out and talking.
I can understand your frustration. Humans are sexual beings. You have needs that aren't being met and you're at your wit's end.
Divorce can be very ugly though. As you said you wouldn't see your daughter as much, plus the division of property and money and all that yucky stuff...
But affairs can also be ugly.. or even lead to divorce. You might catch something, you might get caught, you might get away with it... it all depends.
That's why I suggest telling your wife how you feel. Don't just tell her you want more sex. Tell her you love her and your daughter. Let her know you want to remain a happy family. But you have to tell her plainly that you need to have an active sex life. You can eve ask her if she'd rather you go out and get it somewhere else. That actually is a possibility that she may be OK with (it might be rare, but I do know a couple that way). Tell her you love her and you crave her sexually. You can also ask her if there's anything she'd like you to do differently or something new to try for her. Don't forget, sex is a 2-way street. You can't be the only one expecting pleasure out of the deal, you need to ensure she's enjoying it too.
There's plenty of tips throughout this site to help you with that if you need it.
I hope this helps.
Keep us posted.