Since the Suit of Cups is all about love and loving relationships, it's easy to see how the Knight can be regarded as the lover of the cards. When representing a moodshift, the card can indicate the period where a man falls in love.
When it represents a person he will be a complex and highly emotional being - creative and visionary, sensitive (and sometimes over-sensitive), romantic and intense. He will give the impression of being open and caring, though this is often misleading; the Knight of Cups is often subject to intense insecurity, needing constant re-assurance and attention.
He is attracted and attractive to women, and enjoys basking in their company. He will often be very charming, with a silver tongue and a powerful personal agenda. He will rarely manage practical matters well, tending to place rather more importance on buying two dozen red roses, than paying the bills. At his worst, he can be inconstant, unfaithful and selfish.
At his best, he is loving, generous with his emotions, supportive and tender. He can be capable of high levels of spiritual development, strong in intuition and warmly responsive. When he's on form he is terrific company, having a good sense of humour and a keen interest in other people. He's often an exciting and stimulating life partner and lover - but only at his best!
You see - I said he was contradictory!