Please help

I am in a situation where my lying has gotten completely out of hand and it is destroying the relationship with someone I love whom I want to be with forever. I lie nearly every day as it is my first instinct. I even told a lie about a lie today which has just made things totally spiral. I have been told I am evil, because of my lying, which I know in my heart and soul I am not. I believe I am ADHD but my girlfriend is having nothing of it. I was very depressed in my final weeks in college and had a cloud of melancholy over me due to the Covid lockdown, and now the lying has made things even worse.