1. a physical mark received on the body that stays permanently or for a very long time.
my body is scarred for life
To be 'scarred for life' is to bear a scar or mark as a result of an accident, pregnancy, surgery or psychological trauma which cannot be removed. To be scarred for life is to be marked permanently by something which has happened to you.
2. to be deeply and negatively affected by an event or something/someone
the trauma scarred me for life
To be 'psychologically' 'scarred for life' means that something traumatic has happened to you or you have witnessed something which will have a profound effect on you for the rest of your life. This is often used as a hyperbolic phrase to exaggerate in telling a story of something that happened.