<human>: I'm 17 male, she's turned 18 two days ago(so I think I can say she's my age). I like this girl, that happens to be a friend of mine, that I've known for about  3 years, and what some months ago I started developing a felling for her.
We go swimming together, we go to school together with another guy, that she isn't very fond of, but she's in a different class. And I also give her math lessons, and nothing ever happened while I was teaching her.
She used to have an older boyfriend, that  one year older than she is, and they broke up in September because he quit school without her consent and she felt very mad at him, and for my knowledge they haven't spoken since. The problem is he was very muscled and scary. 
And I'm not like that, I'm fit, not too skinny nor too fat. 
And and her birthday dinner I was very surprised to see that I was the only boy( aside from her family) that was there, I don't know if she had invited any other. So reddit what should I do.

Could you distill the essence of the text into 1-3 sentences?
<bot>: I like this girl, I give her math lessons and go swimming with her. Should I tell her how I feel?