Is it weird to have a work brother?

I don’t do work wife/husband, but there is this one guy, younger than me, at work that people constantly ask if we’re related (we’re the only Latinos in the department). We always play it off, sometimes acting like we’re long lost siblings, and just have fun with it. My boyfriend doesn’t care and I share the our stupid and funny conversations with him, but one of my friends says it’s a gateway to cheating.

I don’t see the guy in any romantic way, and he has said I’m like an older sister to him. He asks me (sometimes my boyfriend) for advice, we talk, we fake argue, and when we work the same sections we vibe to the same music. I don’t see it as cheating or a gateway to it, him and my boyfriend are cool too and I honestly feel like a big sister to him.

So… is it weird?