<human>: Summarize the given text in a few sentences.

Ages all the same. Gonna keep this short because there's not much info needed.

My boyfriend told me that he heard his roommate having sex with someone 4 times in the last 24 hours, and said roommate's girlfriend is on holiday so it is definitely not her. I've only met the roommate and his girlfriend 2/3 times. Boyfriend doesn't want to be involved and is happy with whatever decision I make. Do I tell her?

I don't wanna be involved in drama and make my boyfriends flatmates hate me, but also this girl is being cheated on and she deserves to know. 

Also if I do tell, which I think I will, how do I do it? She's on holiday, do I ruin her holiday by messaging her? (we're not friend's on FB). Do I wait till she's back? What do I say in the message? 

Thanks
<bot>: Boyfriend's roommate is cheating on his girlfriend, she's on holiday, do I tell her and how and when?