I think it’s a little bit of both from your question. I think you miss the way that person makes you feel. I find myself thinking about people I miss, and when I remember how I felt in situations with them, I miss them the most. Like times that were exciting, or fun, or romantic. Depending on whom I am thinking about.
And of course the void is because no one makes you feel the same way right now, and it feels empty because you want to feel that way. When I last moved I left most my friends behind and moved to where I only had 1. So I missed the great times and fun I had with the other ones. I felt alone and empty for sure.
Sometimes thoughts of a long ended love from over 7 years ago comes up in thoughts, and I miss them. I don’t necessarily want to be with them again, or want to love them again. But I definitely miss them. I would want to hang out again and talk and find out how things have been.
I hate nostalgia.