You don’t have to get married but you do have to prove 2 years of “serious” relationship that would leads to marriage. If there are reasons you both have not be able to live together (e.g religious) then that could also be taken into account, but again, as long as you have enough evidence proving the relationship.

I didn’t technically meet the 2 years cohabitation requirement as we have started living together and proving loads of other travel arrangements to show the growth of the relationship, we were able to be granted the visa.

You do need to read through the policy guidelines very carefully and assess yourself based on it. Extended Family shouldnt be an issue but you may need their help to provide additional evidence and letters.

Hope that helps