Il se sent seul, malgré son chien ?
il manque de compagnie ?
Il est seul doesn't quite cut it. Lonesome from the context has sad or forlorn connotations.
en dépit de ?
Thank you piguy3, added!
Why not sa chienne?
Added. I've just been informed that changes made can take up to a week to be recognized by the system. If there is a problem after APRIL 9th 2018, please report it! Thanks. https://www.duolingo.com/comment/26750687