I don't know if it is cake eating. You're allowed to want a couple of different things at the same time - or perhaps want one thing - an intimate committed relationship - and see a couple of different paths to get there. It would be different if you were in a sexual relationship with more than one person and they didn't know about each other, or even if you were in MC and actively working on things with your H - but it looks like in your situation you have a good amicable co-parenting relationship and there are no immediate plans to reconcile. So you can be open to a conversation about that in the future without living as a married woman in the meantime, right?
I think you're right to set boundaries about your time. Laying aside not being a doormat to your H, it is important for your daughters to know that plans made are important, and you can't ditch someone when you get a better offer, and it isn't okay to play one parent off against each other, and that passive aggressive communication isn't acceptable. You can't teach your H these things, but you are allowed to teach your daughter.
