Centering

The pendulum swings around a fulcrum. As long as the fulcrum is intact the swinging does not create a problem. In fact it is enjoyable.
In human affairs, centering plays that role.
When we swing to an extreme of independent behaviour, as if the rest of the world does not exist, or if does, we have no relationship with it, then we feel a high which soon bursts. the deflation in mood is loaded with guilt of the earlier position (that the rest of the world does not exist .....) We then want to hurt/punish ourselves very severely. The suicidal swing to the other extreme.
This is what your friend is going through.
The solution in the long term is to find the center through meditation. This allows us to find our rightful place in god's scheme of the world.
In the short run one needs a loving hand to hold on to and to gently guide one towards centering/meditation.
Can you play this role for your friend?
Lots of love (you will need a lot of it)
Ganoba