Replying to Asking girls about previous sexual activity...

Ok, so my friend and I are having a disagreement.  I am dating this girl and my friend says that i need to ask her about what he has done before, like how far she's gone.  I told him that i would rather not know and that it seems impolite to me to ask a girl that and that i am generally uninterested in any of her previous activity.  He said its important because you need to know if you are gonna get some disease or something.  I told him that if we ever reach that stage in our relationship, i'll find out, but for now, i don't really care.  He said that she even told him about what shes done and that its not that big of a deal to ask.  She told me that it's not a rude question at all but i still don't want to find out.  Am I trippin or what?
oh, and by the way, i know this sounds like some straight 6th grade shit but whatever.
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