Hi quasar, I'm sorry things have been so hard for you
Depression can be just as severe whether you've had trauma in your life or not, so please don't feel guilty about talking about what's going on for you, in fact it's good that you're speaking out about/sharing with us the way you've been feeling!!!
And you've found a great place to do that, lots of really understanding and supportive people on here. You're not alone
Now you know that you've withdrawn from things/friends/activities, which can be completely "normal" with depression, but do you think there's a chance you might be able to step just a little back into those things/seeing your friends??? Maybe you could get a little support from those friends as well??? If that's hard right now though that's OK.........maybe a family member you could talk to???
Although if you feel the thoughts about suicide could lead to actions please get some immediate help, hey?? Whether that's from a crisisline, hotline or pdoc............just someone, hey??
Now the therapy you're in is good, but maybe it's focusing on the wrong things if a big part is about finding the cause..........because if it is a chemical imbalance.........trying to "talk yourself out of" that is so unlikely...........but therapy might help you with some coping techniques, a focus on self-care, goal setting, and with managing the SI a little better...........things like that. Perhaps worth talking to your T about how unhelpful it's seeming to you??
And you didn't mention medication?? For plenty of people that can be a corner stone in helping them make real use of other things/strategies in gradual recovery.........it doesn't necessarily have to be a permanent thing either........so do you think you could perhaps talk to your doctor about that??
Anyway, welcome to PC!!! And thank you again for sharing with us, please don't feel hesitant in carrying on telling it as it is/reaching for support........you matter just as much as anyone else!!
And you might want to drop in on this forum for SI too:
Self Injury - Forums at Psych Central
Again lots of really understanding and supportive people on there.

Alison