How is Elyot being hypocritical about Amanda's disclosure of her post-marital affairs?

Elyot has no problem with the fact that he had a few affairs after his divorce and before he met Sibyl. However, when Amanda points out that she, too, had a few affairs, Elyot grows angry and disgusted. According to him, it is not proper for women to be promiscuous, though he cannot give a clear answer as to why it is okay for men to be that way. More than anything, it is probably a bit of jealousy rearing back over the idea of Amanda with being with another man.