So, based on your other post, you are some married guy's piece on the side. (Did you think people were too stupid to get the connection between your two subjects?) Based on your other post, I got the idea he was no longer living with her (you wrote she caught the two of you in his apartment. Or was that an apartment he shared with her?)
He says he's unhappy,
That is what every piece on the side says here when trying to explain their lover's cheating on his spouse. When will you women learn that they say this just to get into your pants?
As for him being a Cancer, I would agree. He is a cancer and you need to cut him out of your life until he gets divorced and is available. Even then, I think I would suggest you stay away since deceiving you by not telling you about his wife. (And I agree with the poster about the foolishness of believing in astrology. What a racket that is.)