SPOILERS. Regarding Motive for crime

I have recently completed the whole vn, i havent read the manga or reread it or anything plus i at first didnt pay attention to details so im very confused at alot of things so dont mind guys.

The point is that i rlly dont find the motive for murder for Beatrice's/yasu very plausible. Like ur crush just betrayed u left u alone for 6 yrs. Thats just it..i mean i understand that shes had it rought but not to enough the massacre the whole family and have this insane murder plot. I understand shes got other problems and issues too plus shes mentally unstable,but thats just it. Then shes just a psycho woman. I dont understand why battler forgave her and understood at the end..plus at the magic ending, the boat scene happened in real world i think. So how did he just forgave the random woman who just massacred his whole family!