Your 19, living your own life, making your own decisions, and doing what you want. Just be honest with your mom, and tell her, so she can at least know the truth and can have the time to deal with it. Better you, with no stress, than come as a shock, under worse circumstances.
Your grown, so its your life, and as an adult, your actions will either bring blessings, or consequences. Either way, that's for you to deal with.
Good Luck!