Have name-changed for this.
Before we met, I was in polyamourous relationships. My previous partner had conviced me to do monogamy, which didn?t go well, so we went back to an open relationship when we should have just split up. About a month after finally splitting, I met DH, had the poly vs monogamous chat, and decided to give monogamy a try because ?he didn?t think he could handle polyamoury? and I was still on the rebound from the ex. (dumb, I know!)
We?ve been together for 10 years, married for 7, and have a child who is almost 4.
Periodically, we revisit the open relationship idea, generally when I get a crush on someone.
This typically ends with a chat and a ?no way? from him, though this summer it ended with the question ?what do you hope to get out of it??
Basically, I just want to be single and independent and unencumbered by responsibilities (he would be resident parent, and I?d have our child for a day at weekends, and look after the child the 2-3 evenings a week that he is out doing his hobbies.). I don?t want to be a Mother anymore, it?s hard work and I?m sick of it and sick of being the main parent. He can manage when he has to, but doesn?t often manage to take our active child out of the flat when I?m away for a day or weekend... DD always comes to me, ?mama? is her code for ?I want comfort and/or food? as she knows that I am the responsive parent. We spent a few days with friends over Christmas/New Years, and they commented that when I?m not around, DD wilts a bit and just sits and watches TV or plays on her own; DH does not play with her (he does sometimes at home, but not nearly as much as I do, apparently)
I don?t want to have a DH who wants me to kiss only him (perfectly reasonable and normal for a relationship, but I don?t want that anymore. I don?t want to accept it anymore out of love for him anymore, it?s not enough). I keep getting crushes on people (have had a crush on someone other than DH more often than not over the last 6 months or so.) This happened with the ex, too (it was a distance thing and a few weeks before I was due to see him, I?d start a new fling.) but this time around, I think it might be a sign that things are over?
We did have a talk about me leaving this past summer (which is where the ?what would you get out of an open relationship? Q came from), and the idea of DD staying with him was discussed. I know that I don?t have time for a ?proper? new relationship- but I don?t really want that, I want to have fun. Probably just fooling around, rather than actual sex. I know I prob sound like the ?twattish ex? to a lot of MNers... dunno, maybe I am being one 
How do I do this? How do I leave him, when do I...?
Complicating matters is that I am on consultation for redundancy at work, so CAN?T afford to rent a room somewhere until I have permenant employment (in my mind, I'd leave him with the flat and DD). We have a mortguage. A child. Our lives are basically entangled, and I want to loose it for... fun? The ability to be irresponsible? The attempt to seek happiness? Am I being stupid, or just realising that what I've got isn't working for me?
I feel like I?m in a situation where I basically hurt him by going, or hurt him by staying and cheating
And I don?t want to hurt him at all! Any advice?