Do you have any suggestions to help me move on from this guy I like?

You don't have to move on. It's actually good that you are expecting to not end up with him, so it's not sad if you don't end up with him. If you feel insecure about yourself and think you are unattractive, maybe someone else (he) doesn't. I don't know what you look like, but I am sure you are beautiful. even if you aren't on the outside, I am sure you are on the inside. I see you want to but don't want to move on. Just, admire him from a far. Just, don't lust after him or fall too hard. If the moment ever arises and you find out that he likes you too, tell him you like and and take it from there. I realize how awkward it can be if his sister is your friend, but don't use her for him. Be friends with them both. Hopefully, you and he can at least be friends, maybe even good friends. Who knows, maybe he still has feelings for you, too! Good luck!! (Oh... thanks for answering all my questions. I really appreciate it.)