Engine damage because of cold water on hot engine?

Hello dear ones, I have a huge problem and hope you can help me a little. Situation was this: I got his old car from my father last year. However, it is still registered on his name (today) Since I am still in the process of driving my driver’s license, my then friend was allowed to drive with it. Although only in my company, but nevertheless ^^ My father explicitly pointed out that the coolant hose had a small crack and we should take care that there is always enough liquid and with longer distances more often a “motor break”. As far as so good. Shorter distances always super driven. Det car purred like a kitten. Had also “grade” times 119000 km behind it, so I was good things. Well and then a bigger ride was on. 150 km there, there still within 2 days 120 km and on the return journey after about 80 km I noticed then as co-driver that the arrow the radiator indicator was already behind the red area. I then pointed out the good driver and he meant.. “Yes we then drive into the next place entrance.” In the third !!! (as the engine already began to smoke) we finally drove in. Then the engine was off and nothing went more. Then my ex, after which I wanted to kill him already, 20 times for a duration of about half a minute, turned the ignition key, in the hope that the car would start again. A Is this not what cool water was taken out of the trunk and poured into the container for it. About 4 liters. Nja the end of the song.. ADAC has towed. Cooler broken, engine broken. I can forget car if I don’t want to take deep into the bag. But now to the actual question.. Who is to blame for the dilemma? My ex knows all the accusations of himself, I get nothing from him either because I “can’t give him anything” “The car was shit anyway and it did was only a question of time that it gets broken” … according to his statement. Can I actually charge him for it? Bzw my father, because it is still his car after all. What do you think about it? Thank you in advance and love greeting Birke1982 Oh and sorry for the laaaang text, I hope he was entertaining