Why would she lie?

Me and my friend kate have been friends scince the 6th grade. We are now about to be seniors in high school. Ivebeen liking this guy in myhistory class for a while now, and had been to shy to tell anyone. the guy and I get along very well and nice sweet an kind,but thats just his character he’s nice to everyone. a few weeks ago I told my friend kate that I liked him and she was like “awww thats so cute”.and now bringing t to the presesnt. me kate and some other friends were in an assebly. me and ate were sitting right next to each other. she was texting someone on her phone and kind of tilting her phone way from me while she was texting like she had something to hide. when she sent the messase I saw my crushes name in the inbox(keep mind that she has never told me hat she like him or even if she was interested).so when we got to class after the assembly kate said “can I tell your crush that you like him?” at first I was like nooo but then I was like whats the worst that could happen so she went on to text him.and he said I was cute and I was so exited. but however after school the worst happened. I went home and told my mom the good news while telling her I got a text from kate saying that my crush said he likes her instead of me..I was so bummed out it felt like someone had just punched me in the stomach. but my mom felt like something was fishy and she told me I should text him myself and find out for myself. and thats what I did I texted him and he sounded like he was so happy for me to be texting and I thought for a guy that dosent like me he sure does sound extatic. and we went on to talk about other things then he said so I heard that you like me and I was like yeah.and then he said that he liked me to..I was happy and mad at the same time.why would she lie?