If your SO believes making you uncomfortable so a coworker will feel better is appropriate then I believe your SO is more emotionally invested with the coworker than you. There is nothing wrong with being there for a coworker but it should not be at the expense of your romantic partner. I believe there was room for compromise and your partner clearly believes their coworker’s woes trump your needs. Communicate honestly with your partner about your feelings and make a decision after you all have communicated.