Too late! Everyone is already experiencing numerous relationships of all different types – friendships, coworkers, bus mates, team members, etc.
What is important in each of these relationships is not a state value (in the querant's case, marriage), but rather the underlying understanding between participants in any given relationship, and how well those expectations match.
I'm reading a lot into this question that isn't being said, but assuming the question is about romantic/sexual relationships before marriage, then the answer is simply "if that's what works for everyone involved, go for it!"
Additional details would be most appreciated if I'm missing the point, but the last things you generally want to do in any type of relationship are base your satisfaction on the expectations of others (especially those outside the relationship itself), and use assumptions and past personal experience as a guide over simply communicating and negotiating a successful relationship in. More active and intention-based fashion.