I realise this is a bit of a 'how long is a piece of string' question, but the situation is very complex. In a nutshell, DH's daughter still visiting us at least every other weekend ('long weekends', at that), at the age of 21, and it makes it very difficult to plan social events or get enough time together as a couple, and IMHO this is also to stepdaughter's detriment as she should be spending time with people her own age and building an age-appropriate life for herself. She seems to be happy at home, so it's not like she needs a 'refuge' so to speak, and although I understand she is entitled to see her dad and hopefully feels welcomed by me too, it's hard to not feel the constant visits are damaging DH's and my marriage.
SD has some developmental delays, which complicates matters, and sadly her father lets her 'backslide' and when she is here she's more like a child (not even a teen) than an adult in behavioural terms, sad to say. I do care about her more than it may sound from this post (I'm constantly tiptoeing in my own home so as to avoid hurting her feelings, in fact), and I worry a LOT about her developmental issues, and about how she is ever going to build a happy life for herself, but does that have to mean I'm willing to sacrifice my own happiness indefinitely? Because I don't think I have it in me to do that, unfortunately. I have to confess that after having understood/accepted that she needed to be a priority when younger, after having always been welcoming, friendly, non-critical and accepting (which I still am) towards her on visits... but at the same time after having waited over 15 years for a time when I, and our marriage, might be a bit more of a priority for DH, I am now coming to feel the opposite... that there will never be a time when SD won't come first, that I was stupid and naive to think there ever would.
There seems to be no way I can couch any of this that doesn't make me sound like a selfish, immature b**ch... which I honestly have tried all these years not to be, but it is really so bad that I'm not willing to accept permanently coming second, permanently being bottom priority, either? Thoughts would really be welcomed, I'm pretty much in crisis atm over the future of my marriage and although it's not all down to this, this particular has come to a head for me lately on realising that she may never grow up, break away and make more of life on her own, and that she may be here every other weekend for ever. (Right now, that honestly doesn't feel like an exaggeration.) I'd really welcome input... thanks.