After two seasons of watching his friends couple up, Dustin finally got a girlfriend on Stranger Things - Suzie. Dustin reveals in Stranger Things season 3, episode 1, "Suzie, Do You Copy?", that his girlfriend's name is Suzie and they met at Camp Knowhere. He gives plenty of details about her but we don't find see who Suzie is until the season 3 finale, "The Battle at Starcourt."
In the season opener, Dustin first mentions Suzie when he returns home from a science camp called Camp Knowhere. As he's showing off his prized creation - a ham radio named Cerebro with the widest radius possible for contacting others - to his friends, Dustin mentions he's going to use it to call his girlfriend. Naturally, Will, Mike, and Eleven are stunned by this news. They instantly press him for more details. Dustin goes on to reveal Suzie lives in Utah, is from a Mormon family (hence the restrictions on contacting her), she was the smartest person at Camp Knowhere, and that she's very cute ("think Phoebe Cates, only hotter"). There's skepticism about Suzie being real when Dustin fails to contact Suzie on Cerebro in the first episode but he maintains throughout season 3 that she is very real.
Mentions of Suzie and her budding romance with Dustin are made once more during episode 2, "The Mall Rats." In Dustin and Steve's reunion scene at Scoops Ahoy, Dustin tells Steve about Suzie. The key thing we learn is that Suzie doesn't mind kissing Dustin even though he's missing his teeth (in real life, actor Gaten Matarazzo has a condition known as cleidocranial dysplasia, which affects the growth of his teeth and bones, and it was written into Dustin's character). Per Dustin's intel, Suzie thinks kissing without teeth is much better.
Suzie's big moment finally comes in the Stranger Things season 3 finale, "The Battle of Starcourt." Dustin knows Suzie is the one to call when the adults need the Plank's Constant number in order to get what they need inside the Russian lab. Dustin once again tries to radio Suzie and, unlike the first time around, Suzie (played by Broadway actor Gabriella Pizzolo) answers. Suzie is happy to hear from Dustin but is confused about why he's calling her and not wanting to talk. So, when Dustin asks for Plank's Constant, Suzie demands he sing Limahl's "The Neverending Story" for her first. There's no time and it's embarrassing but hey, Dustin's in love; he'll sing for that number.
Things end on a high note with Suzie and Dustin, with Dustin confirming his Suzie does exist and that they're in a relationship. Judging by the Stranger Things season 3 post-credits scene, there's still plenty of Stranger Things story to tell in season 4, so keep those fingers crossed for more Suzie (and Suzie-Dustin duets).