I may sound terrible for saying this... but I'd have to say an STD would probably turn me off, unless you could prevent transmission 100% through protection, or be at that point where you love that person so much it wouldn't matter and plan on having a monogamous relationship. That's definitely something I'd want to know about before the clothes came off in the relationship, then I could make an informed decision on intimacy at that point.

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Though dreams can be deceiving, like faces are to hearts; they serve for sweet relieving when fantasy and reality lie too far apart.-Fiona Apple