In this article the Authors face the collusion in couple dynamic, particularly the problem of genitoriality in couple therapy case. In particular they focus the couple formation and the partner’s selection, utilizing concepts of contract or pact between partners, distinguishing between explicit contract (declared) and implicit contract (secret), in order to introduce the couple collusion. The clinical case is an example of multidimensional model of intervention in therapeutic day community. In this article the Authors focus mainly the implicit contract and the secrets, omissions and silent agreement connected with collusion. The therapy makes easier the passage from drug addicted couple to clear couple, processing the HIV problem. Particularly the therapeutical work about genograms has revealed the secret pact based on mutual mandate and family myths, where the couple collusion has been constructed. Key words: collusion, secret pact, parentalship, drug addiction, HIV