Secretly like her, or stop liking her? What to do?

I wouldn't tell her at all. Just let it blow over and just try to be friends with her. It might be a while, but if you wait it will be alright. There is no point to fight the feelings that you have for her, because if you have strong feelings for her it would just hurt you more to try and suppress it. So the best idea would be to like her secretly. Eventually you will be able to be friends with her I'm sure. But I also don't know Lily, so there's no telling how long that would take. I would suggest writing your feelings down on paper or computer. Write a poem, or song (if you play music). Writing down your feelings is a big help sometimes. I hope this is of help to you!