OK, a lot of things...

1) You need physical exercise. Move your body. NOT to lose weight, but to feel good and be less depressed. Dancing, swimming, walking, weights are good to add but cardio is still necessary, in some form. Here is a GREAT blog by a really fat yet gorgeous and super flexible dancer:

danceswithfat | Dances With Fat

So moving is absolutely essential, both for now and for the rest of your life. You must find some way of moving your body that you ENJOY. Does not have to be in the gym, does not have to be too structured, but you need something.

2) Restate the thoughts in your OP as a bulleted list and present to the therapist in the joint T session with the mother.

3) What IS your r/s with the dad?

4) Have the T explain to the mother that she CANNOT commit you to a mental institution. She does not have that power. You are not suicidal, but simply depressed, and lots of folks are depressed and still walk around at large (or stay in bed in their apartments or homes). Ask the T to explain it.

I will have more to suggest but please answer (3) above first.

Sorry you are going through this!!