Holy hell, please do not lie to anybody like this. Tell them you are not interested. If you can't make your words match your actions, you are not worth a damn.“I've just been really busy” means “I'm not that interested in you.”
Don't listen to words. How someone treats you is how they care about you.
Eh. Sometimes there is an intellectual divide. Six months ago I jumped into a relationship and didn't realize how totally not ready or interested in it I was until I realized that I went out and massively flirted with practically every guy that weekend. I often have to observe my own behavior to know how I'm feeling. Maybe I'm not very in touch emotionally? It can go the other way too: I realize I'm interested in someone when I observe myself texting them, stopping by to say "hi," stuff that could be written off as casual but isn't. I may say something is fine in theory but in practice I realize it's not. I'm not perfectly self aware. I wouldn't expect most people to be.If you can't make your words match your actions, you are not worth a damn.