Welcome to Just answer !
I am really sorry to know about all these unfortunate developments in your life since the last two and a half years. My sympathy is with you on the loss of your beloved wife , and it is terrible that your daughter is suffering also. However, this is the time when you have to endure all the pain of past and present and be there to support your daughter in such a testing and traumatic phase of her life , as she needs you the most and your presence will definitely reduce her suffering .
You definitely seem to be suffering from clinical depression ( major depression) , for that i would suggest you consult a psychiatrist and get started on anti depressant such as Effexor XR ( VENLAFAXINE EXTENDED RELEASE) , which is to be taken once a day only , as it has a prolonged duration of action and works throughout the day ,and this would keep up a good compliance as well.
Also , i would suggest you start yourself on Psychotherapy ( counseling) as such thoughts of despair and suicidal ideation are dangerous and need to be fought against head on , and this by you alone would not be possible , and so you will need help of a counselor who will start you on psychotherapy and the best psychotherapy suited for depression is a short course Cognitive behavioural therapy ( CBT).
So, i suggest you start yourself on anti depressant and the psychotherapy after consulting and discussing them with a psychiatrist. Also, a meeting with a psychiatrist would give you strength to face your traumatic past and present in a better way .
I can uderstand what i have mentioned is easier said than done , but it is very much possible to embark upon this , plus think about your daughter , and try to become her strength at this weakest time of her life.
I pray to god that , your daughter starts responding well to treatment and may god give her all the strength and suppport of her father at this time of adversity.
I wish you and your daughter best of health. God bless!
I hope my answer serves your query according to your satisfaction.