Boyfriends best friend

Okay So i have been dating the same guy on and off for over 4 years now but before we even meet i really liked this other guy that turned out to be his best friend so when me and my SO started dating i was always around the other guy, the feelings I had for his friend changed from romantic to friend. He turned into one of my best friends too and we would go to each other for a lot. now i am good friends with his girlfriend so the four of us are always hanging out. The other night we were all at a party together and my boyfriend and his girlfriend went to bed and me and him were the last ones awake. We stayed up for a long time just talking and laughing and we both were very very drunk and he ended up telling me that he loves me and always has and i dont really know what to do. i love my boyfriend obviously and i will always have a place for the other guy in my heart but i dont know if i should tell anyone that he said that. If i told my boyfriend it would ruin their friendship and ifbi told his girlfriend it would ruin our relationship i dont know what to do