I can't kill Berengar though he betrayed the Witchers and sided with the Professor and Javed. But I can see his reasons and he regrets it and I let him live. Adda betrayed as well but her motives (power and fame) are stupid. Okay ;D ... anyway, I guess Berengar should symbolise support for Geralt in his fight with Javed. If he kills Berengar the support comes from his amulett. If Geralt lets him alive Berengar supports him personally... though he seldom survives.