In the future, if you don't have an uninvolved person to vent to, other posibilities would include journaling and calling a listening hotline.

It is tough to blame him after the fact when you agreed to everything at the time.

One option would be to apologize to him for not being honest with him about your feelings and also for going behind his back to Chris. Just apologize, do not dilute the apology by defending yourself as to why you spoke to Chris.

You could say that in the future you still want to do favors (if you do) but from now on you will tell him if you feel unable to do specific requests for him.

And if you decline a request, don't label it as "unreasonable", just say that you can't do it.

Why do you want to continue the friendship, though, if it is true that he only contacts you to ask favors?