The funniest and closest to my heart headcanon about Dustin is that he is a famously bad matchmaker. He is completely delusional and will try to push the strangest combinations of people together. He makes convoluted plots and creates whole fantasy scenarios about the people in Hawkins.
This is only exacerbated after he meets and starts dating Suzie because he thinks he is the master of love now. He's like, "trust me guys. I know true love when I see it. Watch this!" and then proceeds to harass two complete strangers while his friends pretend they don't know him
At a certain point, everyone stops taking him seriously and just ignores him when he stops in the store to watch two people in the grocery store chat about the quality of the onions insisting that they are witnessing the beginnings of love or when he latches on to a couple of background characters in the movie they're watching and insist that they are deeply in love.
When he finds out that Eddie is gay after the events of season four, he immediately latches on to that fact and says perfect, I know just the man for you! He doesn't actually say that out loud, but he does suddenly start insisting that Eddie and Steve start sitting next to each other on movie nights, and that he needs two chaperones for this or that event, or asking Eddie and Steve to meet him somewhere without letting the other know and then not showing up.
Everyone thinks Steve is straight and are trying desperately to get Dustin to Please Stop.
Eddie and Steve have been dating in secret for four months and are enjoying seeing Dustin's plans seemingly backfire and their other friends' second-hand embarrassment grow the more oblivious they act and the more desperate Dustin becomes