I feel like you're just agreeing with me?

Living together is a commitment, but it isn't the commitment OP asked her boyfriend about. It's reasonable to not be sure about marriage three years in. It's unreasonable to be cagey with your partner about it, refusing to talk about a timeline and saying that you'll maybe figure it out down the line. The problem is that she's asking him about the rest of their lives and, rather than saying he can't commit to that, he's making it exclusively about marriage as if marriage vs. fully committing to someone for the rest of their lives is that big of a difference. What he's saying is he's not ready to be married; what he's implying is that he's not ready to fully commit. It's unfair to OP for him to be cagey about the latter. Which is why I asked OP: "After 3 years, are you willing to wait to see if that changes years down the line? Is there any actual indication that it will ever change?"