It is so, so much harder to move out of a shared life than it is to move into one. As it is, people who have a little voice telling them the relationship isn't working have to face some painful possibilities, even if they live in separate places. The ones who cohabit are often sorely tempted to ignore the little voice and press ahead with the home purchase, engagement, marriage, even children, all with nagging doubts unexplored, because that exploration blows up not just a relationship, but a home.
Don't put yourself on that path. Just don't. Hold out till you're sure.
Besides, if you do it because "the other person really wants it," or to save money, then you have all the potential problems I just identified plus a bad precedent of not being able to stand up to the other person's pressure and of letting convenience replace conviction.
Question: I totally agree with your warning about inertia, but I wanted to pass on my story as an alternative view. My boyfriend and I moved in together with the idea that we were going to be together forever, but no concrete plans for marriage. Living with him was eye-opening, because I saw a side of him that I did not see when we lived apart.
We are now planning a wedding, and I can say that I'm going into it with skills and full knowledge of what it means to live with this wonderful, imperfect man.
Not being married while we were working through implications of living day-to-day with each other gave me the option of clearly thinking, "Is this someone/the life I want forever?" and the freedom to say, "No" or (as the case may be) "Yes, I want this, warts and all."
Answer: Thanks. It's not so much an alternate view, though, as a supplemental one. My standard advice is that moving in makes sense at the point where you've decided you want to be with this person for good - married or not - which you had decided.
Though I won't even try to talk people out of it who believe Marriage First, I don't think it's necessary or even pragmatic to wait till marriage to move in, for many of the reasons you state.
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