I fucked up

Ella
Last night at a party with my best friend who is a guy. I was very drunk and began flirting with this guy, call him Tony. My best friend previously had an ongoing crush on Tony and it was very serious, like he used to get sad over Tony and I think he loved him.
 So one thing led to another with me and Tony and I ended up in a bed with him giving him a blowjob. When it was happening I kept thinking to myself you shouldn't be doing this but for some reason I kept going. My best friend walked in on us when I was half naked lying on Tony and ran out. I tried to talk to him after but it ended up with me sobbing "I'm so sorry" over and over. 
My best friend left the party and didn't talk to me until this morning when I asked if we could meet in person to talk. He said he didn't want to at the moment. I know what I did is disgusting and I would take it back in a heartbeat, I'm so upset that I could do that to my best friend and I would really appreciate any advice for the apology or situation.
No judgement please