.can't find the feeling that once existed.
The feeling that once existed can't be found anymore.
楼主也可考虑以下的说法：-
1） The feeling that once existed has vanished.
曾经存在的感觉如今已不复存在
2) The feeling that once existed has been severed.
当初的感觉已经破碎
希望能帮到楼主!:)