Such case are mere misuse of our Criminal Justice System.
As per Statistics on 32% of rape cases see Conviction.
Since,there is no proof to substantiate the allegations made against your finace,the likelihood of favourable judgement is bright.
After your fiance has been cleared of all charges,such false & malicious people need to be punished.
Hence,please file a Criminal Case against his ex-Girlfriend under Section 211 of I.P.C. which punishes people who file false FIRs.