Not even that. You get, if you are a normal case and can prove ownership as yours and not joint, everything that you own. If you own it jointly, there's room for argument about who owns what share but it would usually be divided equally. If it's held to be a gift, it belongs to the recipient.
Beyond that, the parties have to rely on what lawyers call equity. That is, you have to establish that it is unjust that the other partner gets the whole of something. That is commonly a case of one party have contributed so much to the purchase of a house, say, that though it is in the sole name of the other, they should be held to have a share.
The short answer is to get married!
There is no such thing as a common law marriage, as, sadly, many a survivor of a couple has discovered when the deceased was married and never divorced and never left a will. Their property will go with nothing to the survivor but the wife will have an automatic right to it. That is so however long the "common law spouse" has lived with the other, now deceased. The other's only claim may be as a dependent, but that is often uncertain and never reflects the deceased's wishes.