Quick rundown, but a long post....SO and I have been together 5 years. We live in separate houses in the same city, but different suburbs, about 30 minutes away.
I met his kids, now SD16, SD12, SS11 after 9 months of dating. I got WAY too involved at first and made myself and everyone around me pretty miserable. Things are much better since I backed off.
SO has primary custody, shared legal with BM. BM lives 2 hours away, they meet halfway almost every weekend for BM's visits.

I broke things off with SO a couple of times, on a couple of "hill-to-die-on" type of issues for me. SO either realized that these issues were actually a problem, or just wanted me back.....either way, he did the things that I asked of him and we are doing well in our relationship together now. Since this all has happened, I haven't posted much, since things are going pretty well.

Fast-forward to now.....the tentative plan is for us to fix up our respective houses, sell them, and move in together in HisTown (kids in school) in the next couple of years.
By then, SD16 will be graduated from HS and out of the house. She may live at home for the first year if she goes to community college, which makes sense to me. She's a pretty good kid and gets good grades.
SD12 is turning into the pubescent teenagery monster that comes with the age. She's "the nice one" so hopefully it's just puberty and she will return to her sweet self soon!
SS11 has a host of behavioral issues (see past posts for info). It took a while to get him in gear, but SO has been a wonderful advocate for him and has spent countless hours dealing with administrators, teachers, doctors, and counselors so that SS gets the help he needs.

SS11 still poops his pants. On a weekly basis. EVERY weekend he is with BM cuz she's too lazy to have him sit on the toilet. This is part of his behavioral issues and being on the autistic spectrum. He does NOT care that he has a load in his pants and he stinks. He does NOT care that he loses privileges each time he does this. He doesn't like it, but having to wash his shorts and jeans in the toilet each time does not deter him. He does NOT care that the kids in his class think is the weird and smelly one. Yep, he is THAT kid. And he has had numerous doctors examine him, there's nothing physically wrong with him, he just doesn't want to stop doing whatever he is doing to go poop.

SO is telling me a story the other day that he stepped in poop in the house.
Silly me, I assume....."Oh, the dog had an accident?"
NOPE!!! SS11 had a load in his pants and some of it FELL OUT onto the floor where SO STEPPED on it!!!!!
OMG....before I could stop myself, I said, "I'm not living with a house shitter!!!!" (I think it was ThinkThrice's house shitter phrase I used)
SS11 is also pretty destructive, but not purposefully destructive, things just fall apart when he "plays" with them, including, but not limited, to:
Window blinds
Windows
Doors
Wood trim
Tablets/laptops/iPad
Clothes
Writing on walls/floors
POOPING HIS PANTS

Also, I'm worried about his behavior when he starts puberty. Is it going to escalate? Will the pooping EVER stop? I even asked SO if he is worried that SS might get violent as he gets older (he is not at all violent now) and even SO said that YES, he is worried about that!

Also, I told SO that we have a LOT of issues to work through and decide BEFORE we move in together.
SO: Like what?
Me: Finances for starters
SO: What about them?
Me: Let's see....I bring myself and my dog to the table. You bring yourself, 3 kids, and a dog to the table. How should the household expenses be divided?
SO: 50/50?
Me(snorting): Yeah you would like that. Me? Not so much. No way are things 50/50 when you have 3 kids and I have NONE. At least 60/40 with other considerations.
SO: What other considerations?
Me: The 60/40 does NOT include certain things that are on YOU 100% such as kids cell phones, kids meds, braces, trumpet lessons, cheer camp, driver's permits/licenses/insurance, health insurance.
SO's face starts to fall.....

Me: See you haven't thought this out at all, have you? When people join finances, it USUALLY benefits both parties. In this case, my spending would double and yours would cut in half. Uh uh. No way. What I spent on skids is utterly my discretion. And since you're all worked up anyway...I may as well add this....I am NOT taking on additional household expenses so you can subsidize kids' secondary educations. We have discussed multiple times how NONE of the kids have any college accounts, nor does SO or BM have so much as one dime put away. I am not going to sacrifice my dreams of travel so that the kids go to college without student loans.
Oh yeah....and you have to sign a pre-nup before we get married.

SO: WHAT THE WHAT????? I AM NOT YOUR EX-HUSBAND!!!!!!
Me: I know you're not. But you have debt, and that's about it. No savings, no 401K, no money market accounts, no NOTHING. I have all of the above, plus a sizable inheritance from my mother and aunt. Nope, nobody is touching that. I have to protect myself. It has nothing to do with you....I will not marry ANYONE that won't sign a pre-nup.

So, obviously I'm re-thinking the whole co-habitation thing, at least until SS is of age. SO has agreed that NO adult kids will live with us (beyond a first year community college/live at home event)
SO is so much of a procrastinator that it may very well be several years before his house is even fixed up to be in sellable condition, so it would be a moot point....however, should I say something now about it? No sense in ruffling feathers about things so far in the future, but it wouldn't be fair if he did manage to get his house all fixed up and in a year I'm saying...."uh...well....I've changed my mind."