Bro, I feel like I am very similar to you and I think you have low self-esteem and are too hard on yourself. There is not one boxer in the world who has gone his entire career not losing a fight (in sparring, amateur and pro) so don't be so hard on yourself.

Also, about throwing in the towel, I think you already know the answer and you should keep going, maybe find some other stuff to do aside from boxing, like gaming/tv programmes (pro's do other stuff too).

Finally, I would recommend therapy, I have struggled with mental health issues also and I feel that counselling helped me in boxing too as it is a sport which requires great concentration.

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Good luck man, don't be so hard on yourself and take care.