Your horrible experiences with your ex and your friends severely shattered your ability to trust. I think that may be at the root of your isolation, loneliness and despair. I don’t think the answer is to fake it. You do need some help and support to regain your ability to trust other people — and to know who is worthy of your trust.
If you could solve this problem on your own, you would have done it already. I understand that you are trying to protect your mom from worry. But you are protecting her at the price of getting help for yourself. You may also be setting her up for far more pain.
Believe me: As a mother myself, I know that I’d rather deal with worry about my child than have to manage the guilt and regrets and grief if that child hurt herself. Take your letter and my response to her and ask her. I’m pretty sure I”m right about this.
Please follow your good instincts and find a local therapist who can help you.
I wish you well.