First love & confused

I'm 23, and have been with my first boyfriend/first love since May 2013 (around 9 months). He's 27, it sounds like a big age difference, but he looks like a 25 yrs old.

I can't complain about my relationship with him, because he's an awesome person. He cares about me a lot, he tells me and shows it everyday. In my case, I love him as well, and do care about him, and I let him know that too. But this is my first relationship, and sometimes I think about it, and have some doubts. He's more passionated about our relationship than I am. We have even talked about getting marry and having kids in the future and stuff. I mean, he's definitely a keeper, there's nothing wrong with him. I'm just scare because I lose my passion sometimes... I have doubts because of my doubts.... if that makes any sense.

I don't know how to prove myself? that he is the one. I see these other people being in other relationships, experiencing and stuff about being with someone different, and in a way I will like to maybe, hangout with someone else and see how that goes, but on the other hand, I don't want to leave my bf, because, what if he is really THE one? and I'm making a huge mistake?... Is not that I'm afraid of staying alone for ever, nor that I want to struggle in finding love, like other ppl have gone through. YES I'm really lucky that my first bf is husband material, I'm just not sure that I'm really in love love?.... Or maybe I am, but I'm just afraid to accept it? don't know why though.

The way I see it too is that, he has had other gf and have dated other girls and stuff, so he knows what else is out there. I have never dated a guy before, he is my first everything!..... I just feel like I'm missing that part of youth or whatever. I know is a silly "problem" but this is a commitment you do for the rest of your life.

Please, don't think that I'm a dumb girl or something. I just need advice or different points of view of what should I do....
Should I just forget/scratch the idea of maybe hanging out with someone else? (not right away of course, since there is no one else I'm interested at the moments)
Should I just go with the flow of the relationship?... Although I know sooner or later we'll get marry
Am I being just silly?
_____________________? (create your own question here)
what do YOU think?...

No,you are not being silly.

I think it is fairly normal what you are going through.
I think you are putting too much pressure on yourself.
Take it easy. Dont rush into marriage, give it a few years yet.
That way you have plenty of time to discover whether he really is the one, or not.

I think this pressure is what has put doubts in your mind.
Let it all go. Then you will see more clearly what you want

I think what you need to do is talk to him and tell him exactly the things you are telling us.
If what you want is to experience other people.. then you need to do that to be sure... but do it because it is what you want.. not just because he has had other girlfriends.

Some things you could ask yourself.. Are you happy in this relationship? Do you have similar goals and dreams, similar interests? Is this man selfish in any way?
You don't have to be "passionate" all the time to be right for each other.. but what you do need is to feel comfortable and happy.
Can you see yourself having a future with this man? It may be that you just need more time and to take things slower. You need to think about things.. but you really need to talk to him about your thoughts and feelings.