While I can’t attest to why your coworker is angry all the time, I can say that it is possible to feel lonely in a marriage. While you are connected in a functional marriage, your partner isn’t going to be and can’t possibly be the only source for your needs. You’re not going to have all the same interests as your partner and it’s good to have friends outside of the marriage to share those interests. Sometimes your partner will drive you crazy, so it helps to have friends that can help you with that. If you don’t have anyone to help with those needs it can get lonely quickly.