Thanks for clarifying!
Hopefully, since this is the first time it's happened, once your GF and BF get less defensive about the whole thing, you can all recover from this. Still, making sure you and your children are adequately represented as equal members of this household is truly important.
Last week, I was on my away day and get a message that they were going to host their 'first sexy visitor'. My boyfriend had met a woman he was very into at the sex party my partners were at the night before. She was passing though our hometown and my boyfriend wanted to invite her over.
Two thoughts here:
1: You were notified (by text?) when you were away, rather than your BF thinking that maybe it'd be good to talk about it first (given the talks you all had prior to moving in together)? Your BF isn't living alone with your GF any more. There are other people living in the house to be *generally considerate* of. You don't want that? Don't move people in.
2: He met this woman the day before, and... did he even tell her there were kids in the house, or what to expect? Or was she blindsided?
Sounds very impulsive, at least in this instance. Then, when called on it, he got defensive. At least, that's how it comes across to me...
Also his argument is that my screening new people the kids meet keeps the children from meeting new interesting people and that this just shows my distrust in them when it comes to new people.
Um, no. I call bullshit on this. This is someone being defensive and throwing out reasons that this is your fault and not his.
My friends are infinitely more interesting to me than they are to my kids. I don't consider it a favor to them to introduce them to my friends... they probably couldn't care less. And these are my friends!
Strangers? Fuck, no. And I'm extroverted as hell! And my kids are 19 and 16!
This is supposed to be your kids' home too, no? Do they feel like they can be comfortable in their own home if the presence of new people is going to be the norm? Are you going to be comfortable?
One of the worst things is going home to a place where you don't feel comfortable or welcome. I agree with the others - if this is going to be a sticking point, moving out would be for the best.