A Virginia which stays with the Union is not automatically a Virginia which fights the Confederacy.
Virginia staying with the Union will likely be the reverse of Kentucky in that they will declare neutrality like Kentucky did but will be more sympathetic to the South meaning that if Federal's try to recruit troops from Virginia or send troops across Virginia's borders the state will condemn this and demand the removal of these things. In the even of Virginia being invaded by both Federal and Confederate forces they are more likely to condemn the north and side with the south than to condemn both and maintain neutrality.
Virginia staying with the Union will likely be the reverse of Kentucky in that they will declare neutrality like Kentucky did but will be more sympathetic to the South meaning that if Federal's try to recruit troops from Virginia or send troops across Virginia's borders the state will condemn this and demand the removal of these things. In the even of Virginia being invaded by both Federal and Confederate forces they are more likely to condemn the north and side with the south than to condemn both and maintain neutrality.