Why did mole drop hopelessly onto a tree stump and sob?

Mole found the scent of his old home for which he'd forgotten, but Rat wanted to keep going. Mole was devastated but he stayed loyal to rat and did not abandon him.

‘I know it’s a—shabby, dingy little place,’ he sobbed forth at last, brokenly: ‘not like—your cosy quarters—or Toad’s beautiful hall—or Badger’s great house—but it was my own little home—and I was fond of it—and I went away and forgot all about it—and then I smelt it suddenly—on the road, when I called and you wouldn’t listen, Rat—and everything came back to me with a rush—and I WANTED it!—O dear, O dear!—and when you WOULDN’T turn back, Ratty—and I had to leave it, though I was smelling it all the time—I thought my heart would break.—We might have just gone and had one look at it, Ratty—only one look—it was close by—but you wouldn’t turn back, Ratty, you wouldn’t turn back! O dear, O dear!’