SUBREDDIT: r/relationships
TITLE: Me [23m] with my girlfriend [23F] of 5 months are struggling with my co worker who I have hooked up with.
POST: I am a grad student and I moved to a new city where I eventually ended up hooking up with someone in my program. She then joined the same lab as me, which I then told her whatever was happening was over since she decided to work in the same lab as me. 

I was in a relationship that ended due to my move and this hookup happened once and really meant nothing to me. It happened because I was in a new city where I knew no one and was just out of a relationship. 

I told my now girlfriend this and she is uncomfortable with me having to spend work days in the same space as her. I did miscommunicate the amount of time I spent with my co worker because to me just being in the same space as someone isn't really spending time with them. I have no feelings whatsoever for this girl in my lab, and I don't appreciate the fact that she joined the same lab as me, but I can't do much about it. 

Is there anything I can do to help my girlfriend be okay with this?
TL;DR: 
Have to work in the same space as someone I once hooked up with. How can I help make things better with my girlfriend?