Rumor that I’m cheating 🙄

So I was just informed that there is a rumor going around work that I’m cheating on my boyfriend with a coworker. The coworker I’m supposed to be sleeping with just told me about it. We’re friends and have hung out outside of work but he’s really not my type. I’ve been with my boyfriend for four years and and known him for six. Plus my friend just showed me the engagement ring he bought his girlfriend. I’m guessing it’s one of the kids that work at the store that started this rumor seeing how I’m always talking to this coworker from another department.