Still missing my former best friend sometimes

My former best friend is also my ex so due to us having had feelings for each other it got complicated and toxic mix mental health problems into that formula and you don't have the most stable of friendships but he was important to me and me to him. Earlier an amateur photographer in the city here, like myself, texted me on instagram and since my former best friend is also a photographer I got my hopes up for a second it was him who had sent the text "hi how are you these days? :)" even though after a quick look at the account my ex is a far better photographer + he doesn't type the way the person behind the account did and very soon I had it confirmed it wasn't him but someone else from my past. It still made me disappointed. I sometimes get the urge to text him, especially this year the pandemic would be a good excuse like I could just say i'm checking in on old friends seeing so that they're okay... And it wouldn't be so personal... Because he's not the sentimental type at least he pretends not to be. He has this very sarcastic, sometimes bordering on rude, facade that he puts up and I don't wanna be disrespectful because the last time we spoke he said he has nothing against me or anything he just doesn't think it's good for us to be friends anymore and I can see where he was coming from.Naively I had assumed we'd be friends forever. We'd joke sometimes about what we'd look like when old, and I just thought that of course we'll still be friends then... I've never felt that in another friendship so strongly.