Lol it's definitely not rape nor do you need to end the relationship.

You can withdraw consent at any time during sexual activity. OP said stop, her boyfriend held her down and continued. He penetrated her after she expressed pain and withdrew consent. That is, by definition, sexual assault. Rape doesn't have to involve a stranger or overt violence (yelling, hitting, etc.). OP can break up or talk about it. If they talk and he does it again, then does she have your blessing to end it? How many times can a man ignore "sex is painful, stop" before his partner should leave?

Why is nearly every piece of advice in this subreddit always so dramatic?

The advice here may "dramatic" because when you find someone who doesn't respect your boundaries early in a relationship, sexually or otherwise, that is a red flag. If your new partner can't help but continue penetrating you when you've asked them to stop, that's alarming. It's also alarming 10 years into a relationship, but one could argue that if you have a history that long without other incidences it is more worth a discussion. OP has been in this relationship a few months and, imo, if someone in the first few months of dating is both unconcerned sex is painful and ignorant of requests to stop in favor of his own orgasm, that is a perfectly good reason to break up.