Thoughts on being with a coworker???

He super nice. He started working where I work last April. I've been there since last January. Anyways. It took him a while to open up but once he did he was awesome! I ended up sleeping with him last July, December around Christmas and now he's asked if I'm going with this group of coworkers to Mexico this summer (there are like 40 people going). But everyone that's going is either dating someone or married except us so he said if I go I'd be bunking down with him for the week. Is this a bad situation? I mean we haven't shared that we've slept together. Is this ok?