<human>: I've been with my girlfriend for almost 9 months now. We both believe we are the one for each other and love each other very much. I wouldn't trade anything for her. However, I think I unwillingly damaged our relationship. One month prior to meeting her, I had sex with another friend of mine. I lost my virginity to this girl who was just a friend to me. Then about a month later I met my girlfriend and we are happy as can be now. I never told her that I  had sex with that girl because I was too scared of her reaction and also the fact that my girlfriend knows her and is friendly with her. I know I didn't technically do wrong but I just feel like keeping it from her is wrong. But at the same time I feel like I shouldn't tell her. I really need some advice because I don't want to damage what I worked so hard building up.

Provide a brief overview of the text.
<bot>: Kept a secret from my girlfriend but I don't feel it is my obligation to tell her. Should I tell her or no?