Hi Samantha,
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It sounds like you already know your parents' views on the subject...so telling them now is only going to bring the same sorts of lectures and attitudes. Since this has been going on for a while, and they've maintained the same attitude...it's not likely that they're going to change. I don't know your situation completely, or what your parents are like, but I'd suggest waiting...until they don't have power/authority that they can leverage over you.
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Be safe,
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Kay