I do know how you feel - our youngest daughter has moved in to a house with her boyfriend today. She is expecting a baby and they are very happy, and the house is lovely, rented, but totally refurbished and equiped and they have bought new furniture etc., so no worries on that score but ...
my wife is away with work, and I'm here on my own thinking that usually on a Sunday night she would visit friends, and come back about ten o'clock, and we would watch TV together and have a chat, and tmorrow I would take her to work.
Of course, neither of those things are going to happen - which is perfectly fine, but I do know how you feel.
I also know that we will get used to it, and know it's the right thing for them to do. Night time is always worst. First time my youngest went to Browni camp, I told her that at night when she felt homesick and sad, she should tell herself that she is tired, and tomorrow she will wake up and be glad she is there, and everyghing will be fine. I told her the same thing today as I was kissing her goodbye - now I just need to tell myself.