I've come to the conclusion that it's better not to. After 5 years together we've discussed it a couple of times - only very recently we looked into it again, but so many issues came out of the woodwork, even in the early stages that it would almost certainly end in tears. It's frustrating because I don't want to be boyfriend/girlfriend for the next 10+ years, the relationship hasn't moved on at all in 5 years, I still feel like a side-piece!
But the alternative of two sets of kids expecting their own lack of rules to continue unchanged, all insisting that everyone else is getting the better deal, DP getting defensive, me getting anxious, dealing with the discrepancy in income/spending habits, the mess. And that's all WITH a new house, I couldn't bear to think of the issues if you move into an existing family home.
I'm currently reading StepMonster to try and get my head around the difficult relationship (or lack of) that I have with his DCs. I had thought that moving in together might be the making of us, but I have a feeling when it comes to make or break, step-families usually break.
And DP won't consider doing it with a back-up plan, eg renting somewhere to see how it goes for 6 months, he thinks it should be all or nothing. I can't take that risk.
And he wants his ex's mum to be included and move with us, as she lives with him and his DCs. DSD1 won't do it without her grandma being included. Funnily enough, that's a deal breaker for me!
Just don't. The mundane domesticity will kill it if the 'blending' doesn't.