Bro, you dodged a bullet..be glad things worked out this way. Be happy that YOU didn’t buy her a house and a car. Can you imagine if you would have invested 15 years of your life only for her to divorce you later? If she dumped you for him then she will dump him for someone else they won’t stay happy forever. You know 100% she isn’t down to ride. A loyal gf should be down to stay in the car with you if you are homeless.
Honestly, someone bringing over their new partner to an ex to show them off is horrible. As many ads you loved her it’s clear she was a cruel selfish person. I had a partner very similar and it was hard finding out how cruel they were. Once you find someone genuine it’s really light a day between them and your old partner.