In love... with my best friend's boyfriend?

"What do you mean? He's probably just ill!" Kelsey snapped.
"Kelsey, I know you, if he was 'just ill' you would be nagging on at me because you missed your Cody-wody! Where is he?"
"OK, he's just buying something for me. He should be back soon! Why do you care?"
"Er..."
"Never mind. Lets get to class, we'll be late!"
At the end of the school day, Kelsey told me she had to go somewhere.
"Where?"
"It's none of your business!" She grunted.
Cody came up to her.
"Everything alright, babe?" He asked.
"Yeah. Lets ditch this joint."
They walked off, hands intertwined.
I waited for a few minutes and then followed them. After half an hour's walking, they went to the cinema.
"Crap, I have no money!" I cursed.
I stood outside the cinema for three hours, listening to my music, until Cody and Kelsey came out.
I felt like a stalker, but I just had to see what was going on. Kelsey had been acting weirdly for the whole day.
After another hour of walking, the two love-birds reached Kelsey's house.
But instead of Cody walking off to go to his own house, he went inside with Kelsey.
"Shit, please... Don't do what I think you're going to do!" I prayed.
They had left the front door slightly open, so I could get inside without any disturbance.
As I crept up the stairs, I heard noises coming from Kelsey's room.
I ambled towards her bedroom, and peered through the door.
The two were absolutely stark naked.
"Oh. My. Fucking. God. Kelsey..." I breathed.
I could not take my eyes off of the two, as they moved into each other.
When I had seen too much, I ran out of the house and to the park, crying my eyes out.