(Note-- this answer is focused on linear steady-state gliding flight. It is not intended to address a case where the glider is accelerating. Note that a change in airspeed will affect the magnitude of all the aerodynamic force vectors, and note that any imbalance between L and the opposing component of the W vector will make the flight path curve up or down. The topic of how, starting with some imbalance between L D and W, a glider transitions back to a steady-state case where L, D, and W are again in balance (in the absence of corrective control inputs from the pilot, typically via a series of gradually decreasing "phugoid" oscillations involving continual variations in glide or climb angle, vertical speed, airspeed, pitch attitude, and to some extent angle-of-attack) back to a steady-state case where L D and W are again in balance, is a fascinating one but beyond the intended scope of this answer. Likewise the subject of loops and other aerobatic maneuvers, or any other form of accelerated flight.)
