Between a boyfriend and a girlfriend, written contract stating how many dates a week a couple will have, for how long, in what places is an aburd thing reserved for geeky millionaires with a weird sense of humor.
Yet, in truth, almost all social relationships are full of exquisitely detailed sets of expectations and obligations, similar to contracts, but far more flexible, detailed and somehow fundamentally different in character.
People who are dating do expect a certain frequency of interaction. They do have understandings about how outings will be paid for, indeed, there are specialized terms like "going dutch" to describe them that are as specific and arcane as the shipping terms in Article 2 of the Uniform Commecial Code. They have shared understandings about what should be worn on certain outings and whose duty it is to communicate those expectations. They shared understandings about how they are to address each other (sometimes context specific). They have shared understandings about when and how it is appropriate to touch each other. They have understandings about when to buy gifts, and what is appropriate in value and type.
Indeed, part of the point of the elaborate mess of informal understandings required to have a social relationship with someone is to screen people to see if they have enough in common with you to make it worthwhile to trust them. Countless men and women are dumped every day because they don't sufficiently fathom their partner's often unstated informal understandings and expectations.
The touchstones of informal understandings include a constant willingness to amend the understandings by mutual agreement in a way that will better fit changing circumstances, a commitment to reciprocity, and a willingness to excuse with adequate receiprocity -- breaches of understandings that are not the fault of the breaching party. Those involved may or may not communicate dissatisfactions with failures to live up to informal understandings; those who fail to live up to informal expectionations may apologize and acknowledge their breach or not as they wish. Either way, if anyone becomes sufficient dissatisfied with the relationship, they may terminate the relationship or otherwise fail to reciprocate.
One of the challenges of the law is to know when to give legal effect to informal understandings, and when to disregard them as less than the formal binding legal agreement. Written contracts usually signal a desire to opt out of the regime of informal understandings. Business dealings without written contracts, in contrast, require some legal principles to give them meaning, which could be a set of default rules (agreements not in writing are not enforceable), categories (everything is a gift or a transfer for consideration or an accidental transfer and has a legal consequence as a result), or a more piercing examination of the evidence regarding the intent of the parties.
The trouble with the latter evidence intense approach, is that few people are capable, most of the time, of fully articulating what is going on at the level of informal understandings with a level of detail and accuracy necessary to provided meaningful guidance to a third party, even though they understood the informal understandings at the time. In the same way, many people can recognize on face out of many similar ones, but few people can easily draw or even tell someone how to draw that face in a way that would distinguish it from the others for a third party.
No fault divorce is largely a product of a decision by repeat participants in the system that courts were incapable of fruitfully taking evidence that would do justice to the informal understandings present in the intense and expectation dense social relationship of marriage. Fault divorce has virtues in theory, but in practice, is too hard to adjudicate in a way that does justice to the parties.
No fault automobile insurance and worker's compensation insurance, while not drawing on the informal understandings that are at the heart of why marriages die, likewise represent instances when the legal system has decided that the amount of factual inquiry necessary to arrive at a correct answer under traditional liability rules is grossly excessive given the stakes involved in the typical case.