I know exactly how you feel! When my son was born, I couldn't stand the thought of him sleeping in my room. I just felt like we both needed our own spaces. When my daughter was born, though, I had her sleeping in my room, and it broke my heart to move her to her own bedroom. I felt like I was too far away from her.
I'd say start small. Nap in the crib and sleep in the bassinet at night for a week to get yourself used to it. The concern I have is if you continue in the bassinet too long, he could fall and get hurt.
Also, the transition to his new room will be a tough one, but since you're moving to a new place that has three bedrooms, it's a new beginning for everyone and is the best time to separate your rooms. That way you're not waking up in your old room thinking he should be there; you have a brand new space for you and your fiance, and he has a great room he gets to grow up in.
My husband knew how hard it was for me to move my daughter to her new room, so he let me splurge and decorate the nursery to make it easier on me. Putting in the extra effort with the decorating made me feel like I was giving her a truly special place and it really made the transition easier for me.
Anyway, once again I've written way more than was necessary, but I hope something I said will help. I think growing up is harder on us moms than it is on our kids sometimes. :)