Why changes the lift during turning with sidewinds? Why is there relative wind in the wind-frame?
Wind cannot 'attack' your wing, because there is no wind relative to your aircraft, only relative to the ground.  You are flying in still air; the still air in which you are flying is moving over the ground.  

Your path over the ground is affected by the wind, so your first bullet point is correct.  'Wind' (in the weather sense) is the parcel of air in which you are flying, moving relative to the ground.

In your second bullet point, if your speed is varying, it must be due to a change in the controls, resulting in a pitch attitude change, or a change in power setting.  I'm not sure what you mean by "glide angle controller" but that would usually be the pilot.  Your speed cannot vary as a result of the wind, as there is no wind relative to the aircraft.  Only by referencing an external frame of reference (looking at the ground, looking at GPS) can you tell that there is any wind.  

So if you are experiencing any sidewind (or any other wind), it is caused by whatever is controlling the aircraft (pilot or something in the program) referencing something other than the air.  This experience cannot be caused by a constant wind.