My (23m) girlfriend (26f) cries when her ex is brought up
So I’ve been in a relationship with my girlfriend for 4 months now we have some similar interests, and generally get on well and have a decent amount of intimacy. Recently, she received a bit of mail for her ex who used to live in her apartment when she rented it out to him and it made her cry. She told me he ‘groomed’ her by telling her things she wanted to hear when she was in a mentally bad place. He was 9 years older and they knew each other for years but one day he kissed her and she didn’t want to lose, in her words, ‘her best friend’ and the one person who understood her so she let it happen and eventually got feelings. The hardest thing for her she said is he just broke up with her out of the blue and kicked her out of her own apartment she was renting to him and said ‘I don’t want to see you anymore’ after years of being nice to her. She says she hates him and hates that he can move on with his life while she suffers. It’s been hard on me because every time he is brought up which is not often at all she crime and it makes me thing emotionally a massive part is still with him and not me despite them having been broken up since last April (we got together officially in January). I like this girl a lot and could see a future with her in it but recent events have made me second guess that. I understand it’s not her fault but I can’t help but feel this way and I’m not a bad person or wrong for it.
What could this mean?