Be careful with GAL while under the same roof, you don't want to cause a lot of resentment in her. You have kids together so you don't want to just start disappearing every night leaving her to take care of the kids, because that is going to make her quite angry, and make her think you are abandoning your responsibilities. What I usually suggest when you are still living under the same roof and have kids is this- set up a schedule. Tell her you would like to start taking a couple of nights a week to do whatever activities you want and that you suggest she do the same. So maybe her nights are Monday and Wednesday and yours are Tuesday and Thursday. Or maybe you each have one night a week, or three or whatever. The point is to work it out so she knows when you will be gone, and the point is also to be fair to her and offer her the same.
Also GAL can sometimes involve the kids. Tell her you're going to take the kids for the evening so that you can spend time with them and she can have a break.
The idea is to try and give her time and space. You want to be mysterious as well, but that doesn't mean "pretend you're having an affair" it just means try and be more independent.
