Handling a break-up respectfully
I think it's time to break up with my girlfriend, but since I haven't broken up with anyone since I was 19, I feel like I ought to handle it better than I did way back then. I was so bad at handling break-ups back then that it took me 5 tries to break up with a guy I'd never been particularly fond of!
A little background. DH and I have been married and mono for 12 years. This autumn a cute girl who he games with hit on him a *lot*. After rebuffing her a bunch, DH finally said (jokingly he thought) "Only if my wife is involved". What do you know? We ended up with an all-around satisfying threesome.
Over time the age/maturity gap has been feeling too wide for DH and I. GF is in her mid-twenties and lives like a young bachelor. We are in our mid-thirties, with a house, kid, responsibilities etc. I'm still happy with the sex, as is GF (I think), but I feel like sex is all we have. GF jumps DH every chance she has, and DH says she's a rather demanding, needy lover, so he's no longer thrilled with the sex. We have almost nothing in common. When she is at our home (which is pretty much the only place we are together -- we can't afford a frequent sitter) GF mostly acts like a guest and doesn't pitch in, doesn't even offer. On the other hand she takes and takes (laundry, sodas) without asking.
It's very frustrating. I know I need to set boundaries, but to what end? She could be a friend with benefits, but what is that if there's no friendship to start with?
When DH and I went into this we said that given the age difference we were going to follow the campsite rule and try to leave GF in as good or better shape as we found her. So I'm not comfortable with just saying "This isn't working. Here's why. Goodbye.". Especially since we see her in small group settings several times a month. The only salve to my conscience is that she has a new LDR who she is very excited about, so I'm not leaving her with no emotional support.
I searched all the tags for any permutation of "break-up", assuming that there would be poly guidelines for ending a relationship in the same way that I found do's and don't's for starting and maintaining one.
Does anyone have any suggestions for how to end this relationship, or at least to move it back down to casual friendship, kindly and respectfully? GF has had a tumultuous year and I'd rather not add to the drama.