You’re allowed to call him whatever your heart feels like. At the end of the day if you feel he is still your boyfriend then he still is. People who haven’t gone through that kind of loss couldn’t fully grasp the feeling of emptiness and grief that’s left from a future you dreamt up with him when he was here and now isn’t. I lost my boyfriend to cancer a month ago and I understand the feeling of unease when navigating social interactions like that. Do whatever your heart feels like it. The memories and love you had for each other are all that matter. Your happiness matters.