1. He introduced his new girlfriend to his ex-girlfriend at a social event, and they all got along surprisingly well.
2. After their breakup, he and his ex-girlfriend decided to remain friends and stay in touch.
3. I ran into my ex-girlfriend at the grocery store, and it was a bit awkward seeing her after so long.
4. You definitely struck a sour note when you brought up Dan's ex-girlfriends during your best man speech.