Sleeping with a best friend who is about to get married

Today I went to a hot spring with my girlfriend, her best friend Suzume, and Suzume's boyfriend. From the first time I met Suzume, I was attracted to her; she is exactly my ideal type of girlfriend. When we arrived, I heard the news that Suzume was about to get married, which made me even more excited. The four of us drank quite a lot, and my girlfriend and Suzume's boyfriend got so drunk that they passed out, while Suzume went to take a shower first. I was also quite drunk, and to wash away the overwhelming urge I couldn't control, I went to the bathroom as well.

When I got there, I suddenly saw Suzume naked inside. It turned out this was a mixed bath. Seeing her figure made all the cells in my body boil. After that, I don't remember what I did...