Some agreements do not deal with these issues, and some paint only a vague picture of the parties' respective financial responsibilities. Other agreements are mind-bogglingly detailed and cover even the tiniest details. In my view, unless someone is spectacularly anal retentive, the less said in a marriage agreement or cohabitation agreement, the better. You wouldn't want every aspect of your relationship governed by a legal contract — - that's exactly the sort of thing that encourages relationship breakdown.