MellowBirds85 it's that kind of ridiculous heresy that will get you toasted on MN !
The VERY IDEA that separated parents would even consider a relationship before their children are adults (and only then with the dc/sdc explicit written permission) is absolutely disgusting... as for living with your bf after 6 months - call social services without delay.
I am a heretic. Met DH in December. Met the kids (mine and his) first time 6 weeks later. Moved in a month after that. Married 18 years.
He never put his kids first, me first or my dc.. we ALL deserve consideration depending on the situation. We have a right to couple time . As long as the children have been looked after, loved, fed and watered.
The argument that 'if she lived with you all the time' doesn't hold up. If she lived there all the time you would know that. You would plan together time by hiring a babysitter/sorting out a sleepover with friends. That's what we did when DH , me and my kids were all at home. (Grown up now) .. if we had planned an evening out and DSD called to say 'can I come I over' the answer would be - not tonight, Squirrel and I are going out/busy/working... how about tomorrow'
It's called boundaries. We all need to learn them. Regardless of being a stepchild /child. Sometimes the adults are allowed to come first. It's called being selfless . Not teaching children this , is to do them a disservice.
OP - I don't think you are remotely unreasonable to ask your DP to put in some boundaries, when you have both made plans for either a couples night in or doing something together outside the house.
If he won't entertain it, then you have a Disney dad on your hands and should run for the hills.