Her mother put a potentially harmful idea into her head. Hopefully she meant that if the female lead started a nonsensical argument, or said something potentially hurtful, not to be stubborn; but to apologize. This conversation was justified. He made his jealousy take over. Even if the male lead had feelings for her; the boyfriend needs to trust and believe that his girlfriend respects him and their relationship enough not to cheat. People and things will always enter your life to test you. You cant steal a person away; they chose to go. He may be insecure because of his own guilt. He is being swayed by his female coworker and is placing that frustration out on his girlfriend. It is in his guilt that he feels if he is being swayed, she must be as well, by someone she is working with constantly. He is watching from a distance and don't know their true relationship. He will find coincidences suspicious. He is judging her for the unknown and potential threat of her leaving him. However, the boyfriend's coworker going after him is known and he doesn't do much against it. Yes, he told her to stop but at this point, he needs to report it to human resources as she is not listening and is going out of her way to be spiteful. She is also making herself seem like a victim, which is quite dangerous. He may put off reporting it and end up being on the losing end. He may think it would be cruel to report her, but having someone do what she does is considered harassment. If she wanted to, the female coworker could report him as an act of revenge. Many times it is who reports first and has a written statement of such past actions as evidence that win. In a case were she to report him, had he done it after, people may think he made it up as a way to save himself and his job etc. That's why it is said, if it isn't documented, it didn't happen. Cruel but true. It is reality.
The main couple seem to like each other but want different things. Wanting a child should have been discussed a long time ago, and just like politics and religion, a difference in perspective on this can be a deal breaker. She should not have to sacrifice her career because of his insecurities. Just as he obviously showed her he wouldn't do the same for her. Back to my main point. She voiced her opinion well. If her mother meant for her to always apologize and keep silent; it could ruin her self-esteem, future career opportunities, and toxic situations could arise from this mindset in real life. I am not sure which the mother meant, but I do know some do hold the standpoint that women should always apologize and keep their head down, and that is not right. It's basically leading your child to ruin. Even if that's not the point she meant, it wasn't explained well, as it is what the female lead interpreted it as. The female lead just needs to voice her opinion while keeping an open mind to her partner's feelings and views. If a compromise cannot be met; the relationship needs to be dissolved. Neither has done wrong so far to be termed as a villain. It's just that they want different things. It's life.