I do think he ought to be punished more severely than the charge for "mischief to property" would allow (unless they never updated that since the times when horsestealing was punished by hanging, and he can go to prison for life for it. But I don't think so.)
Quite possibly this does not fall within the definition of sexual assault, but if so, a new law ought to be made.
He ejaculated into her coffee cup - are there no laws against poisoning that could be used? He made her drink a potentially harmful substance.
The judge should be a bit creative.