How did Tanis feel that he and Raistlin were very much alike?

Tanis felt that he and Raistlin were very much alike in that they let their passions consume them at the expense of everything else. Raistlin left the entire group, as Tanis himself had been tempted to, again and again while in Kitiara's embrace. This is why Tanis couldn't condemn Raistlin, he saw himself as more alike than anyone had guessed.