It depends what you want to say - if you mean that the person has never had a girlfriend and has never been to a party, then “you’ve never had a girlfriend nor been to a party” would be correct, but if you mean that the person hasn’t had a girlfriend or been to a party SINCE a certain date, then “you haven’t had a girlfriend or been to a party since..[the amount of time]” would be correct. I hope this helps!

Do you mean to say, "I have never had a girlfriend nor have I been to a party." ?