It's wrong to abandon someone due to mental health issues.
Don has a roommate Randy who is also a close friend going through a depression and acting more moody than normal.
Don wants to create a more comfortable situation for himself.
Don explains his concerns and talks things out with Randy asking what he can do to help.
Don moves out in the middle of the lease leaving Randy alone and paying more rent.
Randy and Don agree on some things to make things easier for both and remain good friends.
Don loses the friendship and Randy moves on with life and new friends after he beats his depression.