Real World v Perfection
I think there's a large amount of real world realism against perfect world here.
In a perfect world, they could have made the video in the perfect knowledge that neither would release it to anyone without the prior permission of the other and that if one never wanted it released anywhere, only the two of them would have it. Great.
Now, to the real world. Whilst I totally agree that he should be dealt with, in a lot of matters there's a lot of real world 'sense' to not putting yourself in compromising positions, where someone could take advantage. So, for instance, it would be inadvisable for a politician to pay a visit to a brothel for research purposes unless he very openly said he was doing it in advance and was very careful about what happen. People would assume no smoke without fire etc. So, whilst the politician may be acting quite innocently and may genuinely be doing research, they would have rather put themselves in a compromising position and would probably feel the impact of that in publicity etc.
The same would apply in lots of other areas. If someone went and stood in the middle of a road, there could be an argument that anyone coming should be able to stop and avoid them, i.e. never drive faster than your clear breaking distance etc. However, if someone did this and was hit, there might be a lack of sympathy in general and people might think he put himself in a silly position.
So, the same really applies here. Yes, she should have been able to expect total privacy, but this is the real world and she did the equivalent of standing in the middle of a road. If you have a sex video, it might be used against you. If you don't, it can't. So, you take your view of the real world and either accept the risk and make one, or you don't take the risk and decline the opportunity. That's no different than not walking alone at night in some areas of some cities. They're known dodgy areas where people get mugged etc., so don't put yourself in that position unless you're prepared for the consequences.
So, I'm in two minds. Yes, the boy should be punished; no question of that. He has breached trust for the worst possible reason.....revenge. However, the girl did also put herself in a position that many would consider unwise. Yes, that's no reason or justification for his actions. Not in the slightest. But, she has put herself in a vulnerable position, partly because of societies views and prejudices.
And before someone asks.....no, a woman wearing a short skirt (or whatever) is not asking to be raped and should not expect that and anyone who does should be dealt with severely. However, whilst wearing certain clothing in some areas is no justification for being attacked, a lot of women would consider it putting yourself at risk. The fact you SHOULD be able to do it and the fact it is legal does not make it sensible to do it.
At the end of the day, you do have to take care of yourself to some extent in this world and not rely on everyone else following all the 'rules'. Assuming everyone else will behave in the same morally upright way you would, has long been called something. The world is 'naive'. Being 'naive' isn't a crime and never should be, but it can lead to issues. I would suggest the girl here was being just this. No justification for his actions and he should be punished, but naive all the same.