Hello there,
First of all, I am not sure if this posts should be here or in relationships

I am a 21 years old boy.
When I has a teenager, I had little friends, little social life, no girlfriend and no sex, neither a kiss!
When I was 19, I had some more friends, but no girlfriend neither girl friends, I was "tired" of being lonely, and I was tired of "not having fun" having sex. So I had sex with a prostitute, that was my first time, and I had sex with other prostitutes for 2 years.
Now, I have a girlfriend, we have been together for 7 months, we love each other. The sex is great and she is very lusty, and so do I.
2 weeks ago we were talking about our past, I told her I lost my virginity at 19, and that I had no girlfriend neither nothing close before, and she told me we were very different, that she lost her virginity at 14, she had 3 boyfriends but when she was single, she was having sex with friends. And, a week later, we were talking about fantasies, and I told her we could have sex in a forest, and after a few questions, she told me she have already done it 3 times, in a park, in a forest and in a car.
The thing is that thinking of her having fun when she was 16, 17, 18, having sex with friends, having sex in a park, etc. makes me very sad and down. When she told me she had sex at 14, and then she had sex with friends, I couldn't eat for 1 week, I was sad, I didn't have "energy" to do anything, but now I am better, but still a bit sad and down. Then I asked (yes.. my fault) and she told me she had sex in a park and I feel down again.

I think this is kind of jealous or envy, but I know this is something about the past, and there is nothing wrong, and I trust on her. This is something about me.
I think I am sad about my past, about someone (specially someone very close like my girlfriend) having sex and fun when I was not. I wanted to have that fun, I wanted to have had sex when I was a teenager, have sex with some girl friend, I wanted to have a "friend with benefits", go out at night, end up in a park, nobody around and have sex. but I didn't. yes.. this is envy...

I talk to her, but not much, I only told her "I am sad because everyone was having fun, having their first girlfriend/boyfriend, but i wasn't". I don't want her to think it is something like "her fault" or to feel sorry or bad about what she did when she was a teenager (which is fine). She told me to be happy of being what I am now, that the past is sometimes cruel, but we can't do anything about that. Enjoy the present.

What do you think? what can I do? I think writing this made me better

Thanks