I wish I had a solution to offer. If it is any consolation, you are not alone. I also experience increasing depression as nighttime arrives. I'm fine during the day and can put on a brave face, which makes all the problems go to the back of my mind. By the end of the day they come rushing out and I become overwhelmed.
I am in therapy and used to have night sessions for about 7 months. I would be the last appointment usually and sometimes go in at 8:45. Those sessions were so helpful because I was able to convey my nighttime struggles and distress. Now that I see her in the daytime, she thinks I'm feeling and doing much better, which is not the case.

I'm sorry your mother is not supportive of your feelings and depression. I have been fed that same line in the past by my own mother...That it was in my head, I was throwing pity parties and I was feeling sorry for myself... So I feel for you because that lack of validation is crazy-making.

Are you in therapy or trying any meds for depression? Do you have any coping mechanisms that you have tried at night in the past, that have offered some relief? Sometimes it helps me to journal, take a hot shower, come on this forum, read, or do something mind-numbing like watch television or YouTube. I also find it fun to go on Pinterest and imagine the possibilities of life and how it could be in the future for me...sort of like fantasizing about feeling better I guess.

I'm so sorry you lost your best friend for sharing your situation. It's really hard finding people to trust who will not judge and keep you in high regards, no matter what. I never had that until I found my current partner. I've been with him for 5 years and he's the only one who listens and supports unconditionally... It's funny because my family had witnessed that over the years and began mirroring his actions. Now they are more supportive and accepting.

I'm sorry you battle this issue too, it is no fun at all! You could PM me if you ever want to vent or need someone to talk to and I would love to help or just offer extra support and validation. It's terrible to not have a support system.