People getting really hung on tipping and not the relationship issue

To some extent, you and your boyfriend are young and are still learning how the world works. He isn't the first 19 year old to stiff someone on a tip and he probably won't be the last.

But at the same time, you expressed how you felt and instead of being receptive of what you're saying, he's getting defensive. Open and honest communication is needed in a relationship, and finance issues especially. A lot of relationships sink because a couple isn't aligned financially.

I'd also ask to reflect on how his behavior is to others that serve him in public customer service positions. Coffee shop workers, attendents at tourist attractions, rideshare/taxi/bus drivers. Or if in school, how does he treat his classmates, teachers, and other faculty/staff? Does he treat them with respect and kindness or is he brisk and rude?