Mercury represents our communication style and intellectual processes. Strong aspects between your Mercury and your partner's planets and/or points favor communication and sharing ideas.
Mercury Square Sun
A Mercury square Sun aspect challenges your partners way of thinking and their ideas about emotional fulfillment. The question of domestic or sexual expectations become more of an issue. When the Mercury person is square the Sun person you may find it difficult to discuss your ideas although you seem to have not lack of conversation, communication, a meeting of your minds, can prove quite a challenge at times.