So if someone dies and I want the apartment the only way I can get it legally without the landowner's consent is if we're married or "sambo" which is like a shortened word for samboende which means togetherliving. They've got a romantic connotation and basically mean unmarried couples who live together. So if this old lady dies and I say we were sambos who will believe it? How can I verify it before she dies

I'd look into just general legal cohabitation. In many countries it has no romantic connotation whatsoever. It can be friends, family members or just about anyone with a close relationship. It's an agreement you make before the government to recognize that you are both living together and take responsibility for the residence. It means that you both have to agree to major decisions like selling or remodeling the house, carry the burden of managing the household (as in you both have to carry the costs of stuff) and are held jointly liable for stuff relating to the home (meaning that you both can be turned to to fulfill debts and such relating to the house). That might be a better solution but I don't know the details in Sweden.

Also, Sambo doesn't give you any inheritance rights to the house, so I think you're shit out of luck there.

What, how do you know that? 

lads I'm gonna marry her then on the honeymoon she will die if you catch my drift

"Sambor ärver inte varandra. Om din sambo dör, får du behålla halva den gemensamma bostaden och hälften av de gemensamma sakerna. Resten har din sambos familj rätt att ärva. Vill ni ha det på ett annat sätt kan ni skriva ett testamente."

Translation:
Sambor don't inherit each other. If your sambo dies, you get to keep half your shared residence and half of the co-owned things. The rest the sambo's family gets the right to inherit. If you want it some other way you (plural) can write a testament