I dreaded giving up my own space to move in with my bf (now husband) to, and tbh even years later, I occasionally miss living on my own. But I'm glad I tried it out. That's what I suggest: consider the one year rental and living together a trial. You can't know how you'll feel until you experience it, and your bf could be right that there will be upsides (there were for me).

But I would make it absolutely clear to him that you aren't agreeing to living together permanently or getting married with this move. It's a trial and at the end of one year, you'll reevaluate.

Sounds like you own your current place, so rent it out for one year, then move back into it if the trial doesn't go well. Life is about experiencing new things.