Coworker drama

I am working on the Relationships module. I have trouble believing the idea that we control a relationship by what we think about someone else. What if a coworker is not pulling their weight? I’m just supposed to think “That’s fine, I like them anyway”? How is that fair to people who do their fair share and have to pick up slack for that person?

Here is a model on this:
C: My coworker does not reply to a customer email for 5 days that relates to one of his programs.
T: I guess I have to be the one to respond otherwise the customer will get upset.
F: Accepting
A: Handle the customer cheerfully. Start thinking of coworker as lazy and irresponsible.
R: I make it possible for coworker to not have to respond to customer emails.

I also sometimes operate from this model:
C: My coworker does not reply to a customer email for one of his programs.
T: I’m so tired of being the only responsible person around here.
F: Angry
A: Handle the customer less cheerfully. Send coworker a somewhat passive aggressive email about how we need to talk about how to manage inflow of customer requests. Consider cancelling lunch with coworker next week. Mull over how lazy coworker has been. Read judgment into every response coworker sends to me. Consider quitting my job.
R: I tire myself out focusing on other people’s irresponsibility.

I really have a bone to pick on the last R above. Why can my coworker basically get away with murder, while I sit here beating myself up with a model that blames my tiredness on myself?! If my coworker was responsible and did his job, I wouldn’t even have that thought to begin with and I wouldn’t feel tired from covering his work. It doesn’t seem fair at all, and I don’t like how the model always puts the blame on ourselves. It doesn’t hold other people accountable for their actions at all. I guess I should just start ignoring my emails too since my coworker gets off scot-free doing it.