I accidentally ruined my roommate's relationship

I (28M) am currently living with my best mate (26M) and I told him I needed to hold a family event at his place with his permission. He said it's fine and that he and his girlfriend (26F) won't be home. It was a family reunion for my side, a family get-together kinda event. I got all the necessary permits from our landlord. My friend said the event is fine as long as I clean up after. The people who attended barely made any mess, but I cleaned up after them anyway and we all went home.<br><br>At first I thought everything was fine. My roommate and his girlfriend didn't say anything about it. But when I got home from work today, his girlfriend was packing up her belongings and storming out the door with him behind her. I was confused and he explained that I'd accidentally ruined his relationship. Apparently, he'd told me to hold an event at HOME instead of his place. I didn't know this and assumed he meant his place. I asked him why he didn't say anything at first when he noticed me decorating his place and he said it was because I'd given him strict instructions not to go home until the family event is over. I didn't give him any instructions. I think he's blaming me for this and his girlfriend definitely is. They've been quarreling lately and I think they're using this as a reason to break up. I honestly don't know what to think and I feel so guilty even if it was an honest mistake. What do I do? He's my best friend and I don't want to lose him because of this.