Okay, I'm going to reply as I read.
Your situation sounds like one that can make for a really nice blended family after some time has passed. How long has it been since he & she split up? To gauge how fresh it is for her...
I can relate to your story a tiny bit, not that mine is too much like that, but my DH was separated with his ex for almost ten years when we met. They were still friends, and it made some legal issues easier, and protected her slightly against a lame DP she was with. We had to have the "social/religious" wedding apart from the legal wedding because we all waited til the semi-last minute to get the divorce through, and then beaurocracy held it up in the most dysfunctional way... he was legally single for all of eight days!
And meanwhile I refer to her second daughter as our stepdaughter, but she had that daughter with the DP (while legally married to my DH) so there is actually no word for that relationship. Anyway, I absolutely love my blended family, including the ex, so I'm kind of the weirdo on this board.
I would really suggest that you guys get counseling on this issue, right from the beginning. Why wait for it to become hellish? Do it now. When you say to your DH "you're doing too much for her" he may agree but he doesn't take it seriously enough apparently. When a counselor says "you're doing too much for her" he will probably take it more seriously, be a little embarrassed, and if the process takes awhile he will have accountability to an outside figure. Takes the pressure off you! And if you ever start overreacting to something (it's easy to overreact to certain little things when the big thing is
the problem, but we focus on the little things instead) the counselor will be able to help you put that back into perspective. And will help you both in other ways as well. If he or she is a good counselor of course. With the reconciliation perhaps you've already done some counseling?
I think you're right that once there is a legal arrangement for visitation she will relax on that, the outside structure is probably needed for everyone's sake.
A vague idea... it might be best for you to make more friendly gestures while your DH makes less. She should know that even more than she's part of the package for you, YOU're part of the package with your DH. It's a different situation than it would be with a new wife. But the timing of this is something you should feel out--might be best to do this after the legal thing is set up.
I would strongly suggest that you let go of the small stuff. And like they say, it's almost all small stuff. You guys will
get the legal visitation setup. Then follow that. In the meantime, relax about it. Just be patient. This phase (before the legal visitation setup) will pass and unless it takes a long time, it will just seem like a blip in hindsight, as you watch your SDD grow up. Concentrate on encouraging the legal setup to happen faster. So this is a time where you want to focus on the future, not the present...
You will not need to be selfless in the future. Right now your husband wants
to be selfless --but it's not entirely selflessness either, he's got his own reasons. Let him do what he wants as much as possible. Take a deep breath... even if you don't love what he's doing, not being "responsible" for his actions will be a huge load off your shoulders! He is an individual. Let him make mistakes.
Now reading your second post, it sounds like you are feeling jealousy but not saying so. My experience is that, in a lot of cases, jealousy is a real red flag. It doesn't necessarily mean that your first fear is true, but it does mean that something
is wrong--somebody is not quite trustworthy or well intentioned, somebody is not quite able to hold up their end of the bargain... maybe they can in some ways but not in others... so again, Get thee to counseling!! Channel all your freakout energy into counseling, not freaking out. You are not helpless or trapped. It's just that some things can be dealt with quickly (finding a counselor) and some things will take time (getting counseling to work, getting proper visitation).
I would add that a good boundary for you to put down is that if she wants a relationship of some kind with your DH besides bare parenting, it will have to include you. I think that's very fair. I know if my DH's ex didn't like me, and I didn't trust her, it would absolutely not be okay for him to spend as much time as he does over there. (I can be very unjealous, but when I am
jealous it's serious--and I've always been right, though not always in the ways I thought I was.) So it wouldn't work to say "You have to like me" but... that might be a condition for your DH to know about, and then for the ex to know or not know as appropriate. It's common sense either way.
It doesn't matter what her stance is. The judge will give you a reasonable visitation arrangement. Just make sure to avoid hostility in the meanwhile so that she doesn't try to tar you both... even if the judges don't believe her it would be a more painful experience. So it's good to maintain as good a relationship as possible until the legal thing is setup, but you don't have to be afraid of her power. She's not the one who will control it, a judge will.
Again, for relationship stresses, be patient in the moment and find a counselor.
The problem is that he's in a stressful situation, and he's not ready to handle your feelings right now. He's trying to do the right thing, and he doesn't have the resources to step back and look clearly at what the right thing is. And he isn't able to listen to you because while you have valuable input, he just perceives that as adding to his stress and responsibilities. He's on autopilot. Make your first goal to get him off autopilot, and be patient.
Maybe it would help to see a limit. When can you reasonably expect to have legal visitation? When can you reasonably expect to have counseling set up? How much longer will you have to do this on your own and be patient with your DH doing things the wrong way because he's overwhelmed and on autopilot?
Take it slow!