(I know that we're young and we have plenty of time left in our life blah blah blah..)

Hi! 
So like the title says : I'm completely lost in my relationship..
I've been with my girlfriend for one year and a half now and I don't not what is the next step or what to do now. I love her and since our very first sight we knew that we were made to be together but now, after all that time, I think that my 18 y/o mindset is coming back.. 
Since we are together, I stopped going out/partying and now every day and week-end we are together and all that for more than a year now! 
Now I think I went to move on but the thing is that I still love her and we are happy when we are together but I want try something (somebody) else... Does that make me an asshole?
She is young, very young... and because of that, I don't know how or if I should end our relationship. If I do it, it will be so brutal/rough for her because she is that young. She loves me like no other girl ever loved me and it is the same for me.
What can I do? Help me..
PS: I'm french.. I tried my best for my English to look good.
PS²: If you're wondering, we have sex a LOT and it's all great so that's not the problem (I know about statutory rape, etc.. Her parents and mine are ok with that. )
user
We love each other. Relationship and sex is wonderful. We have no problem in our relationship. I want to try other things. I don't want to break her mentally since she's that young.
assistant
(I know that we're young and we have plenty of time left in our life blah blah blah..)

Hi! 
So like the title says : I'm completely lost in my relationship..
I've been with my girlfriend for one year and a half now and I don't not what is the next step or what to do now. I love her and since our very first sight we knew that we were made to be together but now, after all that time, I think that my 18 y/o mindset is coming back.. 
Since we are together, I stopped going out/partying and now every day and week-end we are together and all that for more than a year now! 
Now I think I went to move on but the thing is that I still love her and we are happy when we are together but I want try something (somebody) else... Does that make me an asshole?
She is young, very young... and because of that, I don't know how or if I should end our relationship. If I do it, it will be so brutal/rough for her because she is that young. She loves me like no other girl ever loved me and it is the same for me.
What can I do? Help me..
PS: I'm french.. I tried my best for my English to look good.
PS²: If you're wondering, we have sex a LOT and it's all great so that's not the problem (I know about statutory rape, etc.. Her parents and mine are ok with that. )
user
I'm completely lost in my relationship, and I don't know what to do.
assistant