You are NOT to far gone. The fact that you care is proof enough. Seeing the therapist is wise. They don't "cure" you but help you find ways to fix yourself, like a mountain guide through a dense jungle. It would be unwise to not have a therapist. Sometimes one can be a jerk ... so find another one. But one may just provoke a thought that surprises you.
It is easy to feel that life is pointless and meaningless. Being atheist removes consideration of there being a higher guide and purpose (but this isn't the place for any kind of religious talk). But do not make the mistake of thinking love is pointless and meaningless!
Why consider love as of value? Love is nearly the only creative emotion. Creative in the ability to make purpose. Research neurologist describe the brain as a 'meaning making machine', reflecting mainly on its function to perceive and structure a meaning.
Love helps pull one out of themselves. Now you need kindness and to receive love yourself. But working from where you are, friendship and compassion needs to be expressed and received ... and if you can't feel much right now, don't let that hinder you from proceeding. Worried about becoming a psychopath? ... then do things opposite of being psychopathic.
The Greeks have several words for love and one is agape. Its root meaning is doing good things for others regardless of a motive or feeling. Doing something to build up another. It is principled love, that is love based on the principle of care and humanity. I mention this specifically because, while good for all people to exercise, it is good for those who suffer loss-of-emotional-feeling because it doesn't actually require feeling. It is the 'logic' of love. One can be kind to someone they have no feelings for. There are other kinds of love such as philia (friend) and eros (lust), but principle love will create happiness and purpose.
Obviously you want help. Why else would you post on this forum? I am not a therapist, nor are there active therapists here. This forum is a collection of people suffering problems of a similar nature. Some just want to vent. Others look for solutions. Some share things that have helped them.
You have learned the hard way of excessive philosophical arguments. People can argue blue is orange and up is down. What you need to do is structure a foundation and build from there. Don't be afraid of making mistakes on the way (if you are) because you can and will make changes as you grow. Believing there is no purpose is what an enemy will do with torture to a captive prisoner - breaking them down. Philosophers, often intent on proving how clever they are, break down others the same way ... no love from these folks as they greedily seek attention for themselves.
Temper learning with patients and humility. "Truth" will be different than where each of us are. It is something you move closer to. There are basic truths of human need and compassion and purpose. So build with positive emotions ... these positive goals.
You list a history and progression. Again, while there aren't trained therapist here, some may be able to offer suggestions that help. Everyone here has problems and fears. And while this forum is imperfect, having ups and downs and occasional trolls like any forum, there are people who care. I've known a couple of the admins here and they are kind. Many members here care ... even if they are at a loss for words or energy to reply to all the threads.
Wish you success in your journey. One can't go back to their childhood but in the end they can construct something even better.