My fiance molested by my close friend of mine

My close friend molested my fiance. My friend used to consider her as sister and was also living as room partner in the past. My fiance also considered her as elder brother. I have lender this friend of mine considerable amount of money. On the day of event , my friend was with my fiance at her room as he and me were to drop my fiance at isbt so that she could visit her hometown for diwali. I was at office at that time and would come after finishing my shift. When my fiance was sleeping , on the pretext of correcting her clothes he puller up her tshirt and sucked on her nipples. My fiance was shocked and couldnt react at that time, wnd pushed her off when he tried to take picture. Later on we dropped my fiance and she didnt tell me about this incident. Once she reached her hometown, she confided the incident to her family, and she after finding all her courage finally narrated the incident. What shall be my legal course of action.