It's not that he doesn't have any friends left. It's just that Tobias shuns them all away in his grief. He loves Rachel, his last desperate cling to being human, so much that the loss of her just breaks him. Sure, throughout the series, he seems so miserable, but he has three things that give him hope:
1. His Friends.
2. The sky
3. Rachel
I think that, he just feels indifferent to the others because:
Jake: He despises Jake, I think he wants someone to blame, and who better to blame than the fearless leader?
Marco: Marco might just say something sarcastic or philosophical at Tobias.
Which leaves Cassie and Ax, plus the Hork-Bajir, which are the only ones he can turn to. I guess he fears that he might be comforted again by someone who is not Rachel, so he drops Ax and Loren, the closest ones to him.