John,it is good to be having such thoughts and not rushing into moving in tog, or marriage thoughts.
Everyone maybe getting on like a house on fire,days out, overnighters etc are great but it is a huge step away from being a "blended family"
Those I know who have done it always tell me they can't believe how hard it is or how many problems crop up. Usually one person gives far more than the other.
The happiest couple I know is one that only one person the wife in this case had children.
It can be done hey look at the Brady bunch! but needs lots of thought so many little lives are at stake but all can be overcome I am sure.

I agree that living alone you do become used to it, I was amazed at how little time it took for me especially after 35years tog and going from 5 in the house to just me. I do get lonely but it passes and I admit to liking my own space now and routine more than I ever thought possible.
When the time is right you will know.