This act is an abominable and a heinous sin, even though the act did not involve forcing the victim to have sexual intercourse but it is till a horrible assault that will remain unforgettable in the memory of the victim.
Whoever has perpetrated this evil should repent sincerely to Allah by feeling deep regret for this act resolving to never do it again and wishing that it had never happened. Allah the Almighty accepts those who turn in penitence to Him.
As for the victim, if the perpetrator can find a suitable way through which he can seek forgiveness of the victim, this will be much better. But if he cannot, he should keep praying for her asking Allah that He may help her overcome this awful experience and let her forgive him in this world and in the Hereafter.