Personally, as a solo unattached person, I wouldn't be involved with a married poly guy if we could not have any overnights at all. I would not want to feel like a mistress being used for sex and then the guy puts his shoes on and leaves. If it's a real relationship, I want him to snuggle and sleep in my bed with me. I'd want to feel like there is something I can count on, and that what we have is about more than sex. One night a week sounds reasonable. I could even live with one night a month, but to never, ever have overnights would make me feel like I'm in high school, or serving as a sexual release in his life, and nothing more. So I can totally understand Lucy's response.
Having occasional overnights is not too much to ask in poly arrangements, in my opinion. It seems an unreasonable rule to me. I would expect that a partner of mine has his full attention on me when we're together, but of course there are always cell phones in case of an emergency at his home. That being said, I also totally understand Zoe's objection to the overnight stays, since you did let yourself get carried away previously, and Zoe was feeling neglected. However, I should add that it is not your fault she stayed at home alone when you were with Lucy. She needed to be more proactive in giving herself things to do and other people to be with, if she didn't want to be lying there at night thinking of the fact that you were not home.
But if I were you, I would not have accepted any ultimatums. I would have negotiated an agreement between all of you, even though it would be more difficult because Lucy wouldn't want to sit down with the two of you to do this. But I think the first step would have been to tell Zoe that you would be willing to not have overnights for a specific period of time, not longer than you are comfortable with, and then make it clear that at the end of that period you will start having overnights again - but will work out a frequency that would not impact your obligations at home much.
At that point, I would have asked Zoe what length of time she would be okay with. Then I would ask Lucy what period of time she could live without overnights, for a while. I would have let her know that the ban on overnight stays was temporary, and asked her to please be patient and understanding. Then I would settle on a period somewhere in the middle, where you and both women would be comfortable. At the end of that period, then I'd negotiate for a number of overnights per month or week with the both of them again. Each person has to make a compromise; that is what negotiation is about.
To me, negotiating boundaries is much more cooperative and considerate than issuing and kowtowing to rules and ultimatums. As I see it, married people who choose to have polyamorous relationships are also choosing a responsibility to all the people they are involved with, not just their spouses. If I get involved with someone who has a partner, my main boundary for myself is that no metamours can set rules for my relationships. In other words, I do have my own boundaries that need to be respected, one of which is that my relationships will be shaped and determined solely by me and the person with whom I am involved. I don't want to be in a situation where I need to ask permission from someone outside the relationship to let him kiss me, fuck me, take me out in public, sleep over my place, etc.
That doesn't mean I can't or won't negotiate in areas like time management, but it means that the guy I get involved with would simply coordinate schedules with his wife, not have to get permission (which might not be granted). I want to have relationships with an adult, after all, not someone who needs a note from Mommy. So I always ask before getting involved if a partner has rules or boundaries that will affect me. If they seem untenable to me, I would rather walk away from a situation than get involved and be dictated to by a metamour's unworkable boundaries or insecurities. Nor am I interested in the drama of trying to change someone. However, if their rules might be more compatible with my own rules by some tweaking here or there, I'd discuss it.
Regarding Lucy's refusal to meet Zoe, I don't think that's so bad. While I certainly would respect a partner's existing relationship, and welcome a friendship with his spouse/SO, I am not of the camp that believes all metamours should be friends. I would probably have exchanged a few emails, myself, or spoken on the phone with her, but I don't see meeting her as necessary.
Everything I've stated here is just my perspective, with the aim of being helpful by letting you see how someone in your gf's position might possibly view things, and not a criticism.
