Why does Lassiter have to still stay with Tohr, now that he is back with the brothers and on the mend?

He hasn't completed his task yet. Wellsie wants Tor to be happy again. He's not and until Tor comes all the way back with a new love, Lassiter has not won his way home.

Lassiter's task is to get Wellsie out of the In between . To do this he must somehow get Tohrment to let her go .