Is he willing to do the work?
Any mature person knows that to keep a relationship humming, it takes some work. Even if you get along fabulously, usually there are a few hiccups that need negotiating. My ex and I started going to a counselor a few years into our relationship as I wanted a safe place we could work out any hiccups. I equated it to a high-performing car needing more care to keep it running at its best.
A gal pal recently ended a 6-month live-in relationship because her beau didn’t want to work on making the relationship better. He was fine with it as it was and didn’t see any need to improve anything.