Just to add a bit of confusion: It is generally true that the boundary layer flow is outboard on the bottom surface of the wing and inboard on the top. Swept wings, however, bring in another factor. In the area behind the point of max curvature, where the pressure is rising as you move aft - the adverse pressure gradient - the pressure changes push the boundary layer outboard.
This is interesting in that because sweep brings high lateral stability swept wings are often combined with anhedral for the opposite, balancing, effect. You could say, without too much rigour, that in practice anhedral means sweep and sweep means an outward flow of the BL on the top surface.
This outward flow of the BL is one of the factors leading to early tip stall on swept wings - until or unless corrected by an aerodynamic fix of some kind.
Dick W