So-called Marvin claims are badly misunderstood. Briefly, most, cough, civilized states don't have common-law marriage. This means that even if two people are living together like spouses, and/or call themselves spouses, have joint checking accounts, and so on, neither California nor Oregon will consider those two people married. Even if they've been together for decades and all their friends think they're married, if there was never a legal marriage, they are not, at law, married. They can not get a divorce, in which they'd split up their stuff.
But! Every state in the nation will, in fact must, recognize a valid out-of-state marriage. (This was a little dicey before Obergefell, but now it's true generally.) So the first thing your counsel should do, IMHO, is check where you and the other person took vacations. You might not need a Marvin claim at all; you might actually already be married. Some states, mostly in middle of the country, still have common-law marriage, and sometimes the residency criteria and others are amazingly loose. If you are legally married in one state because of a common-law marriage, you are married everywhere in the US, and you need a divorce.
Failing that, some lay-people know or think they know about what are called Marvin claims in California. The name refers to a specific case, and what Marvin actually says is this: The fact that a couple was a romantic couple doesn't disqualify either party from making claims against the other on the basis of contract, partnership, promissory estoppel, whatever. What this means is that you can make the same claims against a common-law spouse that you'd be able to make against anyone else.
Marvin allows for claims that roughly, kinda, parallel common disputes in divorces, but they're heard in civil, not family court. For example, if a married couple ran a hot dog business together, California would presume that the assets of the business were community property (usually, it's complicated), and there'd be a presumption that the value of the business would be split. If the parties were romantic partners but not married, then one party could make a claim for half the value of the business, based on what's called common-law partnership. These are business partnerships, not related to marriage or domestic partnerships. So, it's a more indirect claim in the same direction.
Marvin claims are thus a bundle of weird civil claims, that often kinda parallel the inquiries you'd expect in a divorce. However, I find there's often other elements, that give rise to greater complexity. To take an easy example, suppose Alice and Bill have a house they've both lived in for decades. They fight, Bill gets hauled off by the local cops and slapped with a restraining order. But only Bill's name is on the deed for the house, and so he files an eviction case against Alice. In most counties, evictions and Marvin claims are heard by different departments, usually in different courthouses, which usually don't talk to each other. So Alice should probably file an answer on the eviction, to avoid default, but also file a Marvin claim and ask that judge to issue an injunction preventing either party from trying to hide assets or dislodge each other via eviction or other filings. If Alice just files a Marvin claim, the judge in the eviction case may very well find her in default and order her out. Even once she's gotten the injunction, it still falls to Alice to take that injunction over to the eviction court. But, in most places, evictions are accelerated cases, and default is very difficult to recover from, so hopefully Alice's Marvin lawyer knows enough about eviction filings to be vigilant, and is able to appear in both places.
Similarly, as happens in divorces fairly often too, many people do not understand the breadth of America's criminal provisions. Using the parties above, if Bill sneaks back to the house where his name is on the deed, to grab a toothbrush, he's in violation of a restraining order, which is criminal. Now there's yet another courthouse involved. Bill's counsel needs to know enough about criminal law to keep him out of that system above all else, without waiving his claims to stuff in the house. This is often accomplished with a civil stand-by, but be aware that if you use the same agency that did the arrest, you may get the same officer who arrested Bill earlier, and who will probably be able to find a violation of the restraining order somewhere.
In Alameda county, Marvin claims are heard in the admin building in Oakland, evictions are in Hayward, along with disputed restraining orders, and criminal matters are in an entirely different courthouse, also in Oakland. Each courthouse has subtly different filing requirements, and all have various traps for the unwary. Hayward is also two hours from Oakland in bad traffic, and the RO and eviction dockets often have eighty or more cases a day to get through.
It's hard to believe for anyone who's been through it, but divorces (and evictions) are relatively quick. I know, I know, they take forever, but go try to calendar a motion for the imposition of a constructive trust and you'll get a court date many months after, probably, mandatory mediation. There's a good analogy here to downhill winter sports. Divorce is a snowboard, which lets you get down the hill fairly well if you know what you're doing. Still best to follow the signs, of course, but you probably won't fall in a crevasse. Marvin is a couple of snowshoes and a broken hiking pole. There's a much greater chance you'll stumble, fall in a hole, or be unable to avoid the trees and rocks. A guide is useful for both, but in my experience, a Marvin claim without counsel is essentially certain to be an expensive failure.
As always, salient points here are somewhat simplified, and nothing here constitutes legal advice. If you have or think you may have a Marvin claim to bring, fill out our instant quote fee, and we'll get you in for a consult.