I've decided that I'm going to come out to my mom.
Is there something that has made you decide to come out?
When I was younger, my dad struggled with a drug addiction. Because I am closeted and a bit closed off I think my mom thinks I'm doing drugs.
You shouldn't be ashamed of being gay and it's great if you're ready to tell others. It will let people get to know who you truly are.
Part of me wants my mom to feel ashamed about what she thought of me.
I understand your frustration with your mother, but chances are she currently doesn't know what to think and once you come out to her she will share the belief that you shouldn't be ashamed of being gay. Have you considered that she might not even think you're using drugs? Try to give her a chance.