Search Results: going down on eachother

Hey girl and guys, I really need help quick with this problem! I have a crush on one of my closest friend's cousin and she doesn't know that I like him. Please use the poll and comment after reading the details. Thanks!
Details-
Her cousin is two years younger than me but he acts our age.
We share qualities like gaming, humor, and personalities (we're both the type to be a total jerk to our crushes at first).
I've met him ONCE.
We met at a waterpark that my friend took me to for the day and turns out her cousins were coming. We split into groups and we thought he would go with his brother but he stuck with me and my friend. He was always next to me. We went down a slide that he wanted to go doubles with my friend with and she refused so she asked if he wanted to go with me. He was about to say yes when I said that I was going alone.
We went in the lazy river after that and his little sister tagged along, she yelled back after talking to him, word for word, "Hey (friend's name)! (Crush's name) really likes (my name)!" I didn't even think he knew my name yet. He freaked out and tried to explain to my friend that he meant like a FRIEND but his sister kept contridicting him.
He say next to eachother when we ate ice cream and he started telling me jokes. We're like friends now. He wanted to go on the racing slides and we went next to each other. The most awkward compliment I have ever heard happened just before that, it was hilarious! The slide was up high and it was really windy so I had started drying off and he just out of no where says, "You're like, really dry already. Like your top half is dry so it looks nice." I gave him a weird look and a thank you with a confused tone. He tried to walk with me back to the car (we came in different cars) and tried to say bye but his brother dragged him away.

RECAP:
I like him, he likes me. My friend think I don't likes him. Should I tell her and should she tell him?