When things get too comfortable with my therapist, I always ask myself, "What are the things we are not talking about between us?"
You can have a lot of talking going on about stuff outside of the the therapy room that goes on and on and on while big issues between the two people sitting in the room go unaddressed.
I personally expect therapy to make me a little uncomfortable. What I need is someone to challenge me and to get me out of my comfort zone.
I think we forget that therapists sometimes err on the side of wanting to be comfortable too. People talk about "resistance" on the part of the client but therapists can be 'resistant' too....