Will a demon leave you alone if you ask it to?

NO. Once you give that evil entity an opening, you are SNARED. If you want out, a lot of ugly things start happening. I do not know your story nor know how long you have opened yourself to this demon. Some demons are ultra powerful. Not all have the same power. If I were in your shoes, I would simply turn myself to God immediately. Baptize myself and make a serious confession and sincere repentance. Read the bible daily. Ask Christ to help you. He will. I can guarantee you, HE WILL. Then seek a Catholic or an Orthodox exorcist. They will help you.