Cressida Bonas was with Harry for two years, from 2012 to 2014. It was his first serious girlfriend, Chelsy Davy, who was with Harry for many years, from 2004 to 2009 and then several breakups and reconciliations after that until the romance finally petered out early in 2011.
We don't know why either of these romances ended. It was said at the time with Chelsy that she was freedom loving and not attracted to Royal life at all. At the time their lives were taking two separate paths, Chelsy's into legal practice, Harry into the army/ helicopter flying.
Similarly, we don't know why the relationship between Cressida Bonas and Harry ended.
There is absolutely no evidence that Harry treated her badly at the finish. Months later, magazine editor Ingrid Seward, a friend of Cressida's family, said Cress was tormented by insults on social media and even people in the street going past and commenting unfavourably on her shoes, hair, clothing.
I myself saw on social media and other forums people calling her CressMess and WaterCress etc and making fun of her boho style, scrunchies etc. Chelsy too got called names like Miss Piggy and descriptions like 'a barmaid after a hard night out'.
None of that had anything at all to do with Harry. However, you have to be a tough nut to survive those things, and hopefully Meghan, who is used to public scrutiny and social media, will be able to rise above it.
Cressida is back with her first boyfriend, Harry Wentworth Stanley. Prince Harry too has moved on and I wish him well with his new love.