You know you'll never be with him again, and that's a big part of the wistfulness.
You will be happily married. You will lie in bed with the man of your dreams, perfectly in love and totally committed to each other. You will make long, slow love to each other and you will know, deep down in your soul that you were meant to be with this person for the rest of your life.
He will be yours. You will be his. This knowledge will make you happy unexpectedly: riding the subway, walking home in the rain. You will love him completely.
And yet there will always be that one person. There will always be that one ex you'll forever have a soft spot for.
No matter how in love you are with someone else, he'll always be there. That doesn't mean you don't love the one you're with. It doesn't make your love less authentic. It makes your love more human. No one could ever completely let go of their feelings, especially if your breakup was a mistake, especially if maybe your relationship was a mistake, but you loved each other deeply.
You probably haven't seen him in years. But you Facebook stalked him. And you felt wistful: either because he looks the same and you could slot yourself perfectly into his life, or because he's gone bald, gone suburban dad, gone Trump supporter. You shouldn't feel bad about Facebook stalking him, really. It's normal to wonder about someone who was once so important to you and who still, despite everything, is so important to you now.
Because your relationship with him helped make you who you are today. He gave you a taste of Jack Kerouac wildness and you learned what it was like to be a little bit drunk and a little bit crazy.
You almost married him in Vegas and it gave you a sense of the importance of forever commitment. He got you through a difficult time in your life, and you're still grateful. He was the first person you can truly say you were in love with. And first love dies hard.
Or maybe he was the first person you ever had sex with. That love dies hard, too, especially if it was tender, especially if it was sweet. It's hard to give up on the person you lost your virginity to, particularly if it's the person you lost your virginity with. If it was the first fumbling time for both of you, and somehow you made it through.
It's normal to miss him, with whom you share inside jokes no one else knows, with whom you share an experience no one else can possibly share. It's no reflection on your current love to say you miss him.
Or maybe he was the first person you ever had good sex with. Maybe he was the one who really initiated you into sex. Before him, boys sort of grabbed at your breasts and fumbled for your clit. But not him. He knew what he was doing.
He taught you what a dildo was for; he tied you up for the first time. He knew how to give oral sex, and he taught you how to get it, and how to do it yourself. Everything you can do for the man you're in love with, you can do it because of him. It's normal to miss him, even to miss him in the bedroom.
You'll always have a soft spot for him. You know you'll never go back to him, know you'll never be with him again, and that's a big part of your wistfulness. He's over. That part of your life is over. You can never get him back, but you'll still have your memories of him. And sometimes, it's normal to take those out of the box and flip through them.
It's normal to miss him. He probably misses you, too.