In your opinion, how long does a relationship (boyfriend/girlfriend) have to last?

it depends how close you feel to the person

if you feel close to them after a few months/weeks then you could call it "serious" but it could take a year or 2

like i said,, it all depends on the age, how serious you want to be (if someone was looking to get married then itd be pretty serious) and the person

Well, I don't think length of time two people are together equates to how serious the relationship is. It more has to do with how committed the two are to each other, and how the two people feel about the future together, or even if there is one together.

Ideally, a very long time... how old are you? Expectations are way lower in the teens, like days to weeks, maybe even months, rarely, where I am. Haha.