I'm not going to tell you what to do. I am going to point out the red flags you cited and ask what you would say to a friend who was considering dating someone who behaves like this.
he kept talking about... that i should’ve ditched my bf for him
In other words, he did not respect your relationship when you were in one.
badmouthed not only his gf of a few years
He handles struggles in a relationship by badmouthing his partner to others,
he left her bc she showed signs of schizophrenia
and uses an armchair diagnosis as an excuse to get out of a relationship instead of just saying it's not working for him anymore like an adult.
he kept guilttripping me when i said i didn’t want to be his gf
He doesn't care about your preferences, and tries to manipulate you when they don't match his.