The short answer is, a lot of things. How your case starts – in an amicable manner or not, with the children living primarily with you or primarily with the other parent, with you leaving the house or your partner leaving the house or you separating but both still living in the house etc. – is one of the most significant factors in the ultimate determination of things such as who ends up with custody of the children, what access schedule you have with the children and even what child and spousal support is owed. It is possible to recover from a bad start to a family law case, of course, but it is much easier, and thus cheaper, faster and less emotionally draining to start your case off on the right foot. If you are considering ending a marriage or long term relationship or any relationship where there are kids involved, I strongly recommend that you consult with a family law lawyer before you do so.