There's plenty of reason, and its all to do with trust. The way she handled their previous relationship was cold and cruel, simply put. She didn't treat him as an equal, she treated him as an afterthought.
Treating him as an afterthought would be ghosting him. Or telling him the day before. We don't know what was said or how it was handled. Holding 'not knowing how to tell you partner you're moving overseas and taking three weeks to find the words to do so' against her is fair. She deserves to be held accountable for her actions.
She didn't make a mistake, she made a choice. Then she compounded that choice but not talking to him and dropping it all on him at the last moment like a bomb. This wasn't a short relationship, they had been together for seven years and she walked away like it was seven weeks.
Yes, and that choice was a mistake. Also, we don't know what the job was. Was this once in a life time research? Did she join ISIS? Was she building houses in third world countries? Or did she just move to Germany to be an HR manager.
Realistically, is the difference between telling your partner the relationship is ending in two weeks vs telling your partner your relationship is ending in four weeks so large that forgiveness is insurmountable? Are those 14 extra days really so dastardly? I don't think so.
Also, the choice wasn't cruel and there's not enough information to know if it was cold. She didn't take the job to hurt him. This wasn't some big scheme to cause him pain. And there's no evidence to suggest that it leaving wasn't emotional for her as well.
What good is not forgiving someone on principle? Or even not giving them the chance to be forgiven? What good is cutting off such a large part of your life for no reason other than she fucked up five years ago.
It's not like he has a wife and kid. In that case boo hoo so sad she lost her chance. But it's five years later and they aren't over each other. He's almost 40 and hasn't gotten back in the dating pool.
I just don't think it's fair to assume the worst about her and the best about him. When they're both probably complicated people with complicated emotions.