Sun Trine Mercury love Synastry ~ Understanding Attitudes
The Sun is the source of all energies. These energies stimulate the activities of the houses occupied by the transiting Sun and reinforce or weaken the planetary effects, depending on the Sun's aspect to the natal planet. When the Sun transits an inner planet, it may trigger a dormant aspect between that inner planet and a slower moving outer planet. If a planet is being transited by another planet when it is being transited by the Sun, the effect of the transit is strengthened.
Sun Trine Mercury
A Sun trine Moon aspect gives your relationship an easy sense of understanding. Your interest in each other is very stimulated, you find that you both can talk freely, and each is eager to listen to the other voice personal opinions and cooperate with your partner. When the Sun person is trine the Mercury person, you will find that you think well around him/her, more articulate and assured of what you say.