Why does my second gear grind all the time and how can i fix it?

-It is grinding because the synchros are more then likely going out. When they get old and wear down they don't slow down the gears as well so the gears dont "lock" together as good as they use to.

-Solution would be to get your tranny rebuilt or purchase a new tranny. Or some have found that replacing the transmission fluid with BG Syncroshift, Penzoil Syncromesh, or GM Syncromesh makes the transmission feel a lot better and shift a lot smoother.
-Also your clutch may be out of adjustment, linkage’s out of allignment or maybe bent. Bad throw out bearings can cause shitty shifts as well as bad bushings or leaky/bad slave cylinder.