But we ARE getting your point. We all just disagree with your reasoning. You say it was a 'sudden bolt of lightning' decision. We're saying, many of us from past experience, that it was not 'sudden' for him.
Think about relationships you've had that you ended. Weren't there doubts before you broke off? Didn't you 'play along' or at least keep the doubts quiet until you were absolutely sure about needing to get out? Even if you pushed those doubts down, you knew they were still there. Or perhaps a friend's relationship she confided in you about. I can guarantee you that my abusive exH was absolutely gobsmacked when I told him I wanted a divorce. But in reality I had been 'playing along' whilst building up to it for months. If you had asked him, he would have told you it was 'so sudden' and that 'I didn't try hard enough'. But I knew better. And obviously I'm not saying your relationship was abusive in any way. But it's no different in that I was thinking about it for a far longer time than he ever knew about.
And the fact that there are now TWO things that might have been weighing on him (moving in AND a joint holiday) could very well be the reason why he chose this particular time to 'dump you'. It all simply became too much, and the future became 'too real' for him.
As far as 'leading you on' by looking at houses and seriously planning a future, if he had serious doubts, then yes he did. He was 'future faking', letting you believe 100% in something he did not believe 100% in. That was very unfair of him. But it's probably something we all have done to some extent when we're trying to figure out whether or not someone is right for us.
I'm just talking from my own perspective/brain and what I can imagine myself doing in that situation. If I was that attached to someone, and if I genuinely couldn't imagine my life without that person I would not just give up on them due to the fact that they had children.
But that's YOU. Not everyone would do what you would do. Not to mention that since you still want him, naturally you'd tell yourself that you 'wouldn't give up'. Because that is what you want him to do. But what if he had told you that you needed to send your children away, because he wanted you but not them. Would you really have 'not given up on him' in that situation? No matter how 'attached' you were to him, you know that you would have NEVER done that because it would have been anathema to you. It would have gone against everything you are. He's made the same decision 'in reverse'.
And it may very well be that he really tried to put/see himself into the 'stepfather' role but in the end just couldn't do it. As I said before, you can love someone to distraction but that doesn't mean that they are right for you. If he doesn't want children (whether now or ever), or perhaps doesn't want stepchildren, then he shouldn't force himself into a relationship where they are involved, no matter how much he may love the woman he's involved with. I chose to never date men with children because I didn't want to be a stepmother. I'm lucky in that I discovered it early on, after a 'non-serious' relationship with a man with kids. But there was a period of time between 'Is this what I want' and 'No, it's not'. The difference is I never 'future faked' by sitting and spinning dreams with this man.
But the bottom line is that he HAS made this decision and you will simply have to accept that no matter how you may disagree with it, it is his life and he had the right to make that decision. In the end he didn't owe you anything, except perhaps a sincere apology for wasting your time and breaking your heart. And all the 'what ifs' and 'I think he should haves' are doing you absolutely no good. It is what it is. You need to put your energy towards moving on, not towards dissecting every thing he said and did, picking it apart, and comparing it with 'what you would have done'. If he didn't explain it to you clearly when he broke off with you, you'll never know his true feelings. Don't waste another iota of your emotional energy on him and on questions that will never be answered. Put that energy towards yourself and your children.
Are you still able to take the holiday, just you and your children?