If you love her, you will be happy for her that she had some
good times with another guy. Sxx is important but it is not
everything. Why do you regret you did not give you "V" to her? So
what if you did? Will your relationship be better? Focus on your
relationship with her everyday and use all you intelligence to make
it wonderful for the both of you.
Your regrets and whatever else is in your head, let it stay in your
head.