The fact that he appears to have lost interest is fully tearing me apart?

Ignoring people is rude, even though you are shy, it is still rude. You keep giving him mixed signals, no wonder the guy is confused and it's hardly surprising he ignores you. Remember, you reap what you sow. If you ignore people, they will do the same to you. Carry on as per normal, if you see him give him a polite hello, if he stops to chat, then chat with him and see where it goes from there.