A friend is asking me for dating/relationship advice. Am I wrong to think that relationships are completely transactional?

In 20s and 30s, they are often about sharing space with someone else. If someone is unwilling to share space, especially when rent is so costly in most cities, is it possible to have a relationship? Does that mean a relationship is just about saving money with someone that you enjoy being around.

if that's true, how much does whether sharing a bedroom with siblings growing up affect the probability that one will be in a relationship?

Would not sharing an apartment with a potential partner limit the dating pool severely as potential dates are going to put their roommates above the potential partner on the social priority ladder.