Is it normal that my best friend and girlfriend are meant for each other?

I have been dating with this girl for a few months already. I admit that I was caught by her looks at first, but it was her personality what truly charmed me. She is the nicest girl I have ever met, she is one of those people that always do nice things for others and is incapable of hurting anyone.

So, things got serious and I decided to introduce her to my friends. Everyone liked her inmediately, specially my best friend. My best friend is also like the coolest and nicest guy alive, sometimes I even feel unworthy of his friendship.

The thing is that my friend and my girlfriend now get along well... too well actually. They have lots of things in common, almost everything in fact. They have the same hobbies and have the same taste in films and music for example. But the strongest point is that they are both truly kind people. I am not nice like them, I am too selfish to compare myself to them.

We have been doing many activities as three lately. I can't help but notice that they have so much chemistry together. They have a very similar humor and can hold extremely long conversations without even noticing it. When I speak to them in private they always say nice things about the other. I thought they were just trying to be nice at first, but I noticed that they are totally sincere.

I think they are meant for each other. I like my girlfriend a lot, but I am definitely not the one. We are not compatible in many things and I can't hang out with her for too long (because we get a little bored). We have been together for a while and I still don't picture us together in a distant future. I think that my best friend is her true soulmate.

I know that they would never have an affair. In fact, I don't think that they would even admit their feelings out of loyalty for me. I still have many feelings for my girlfriend... but I was wondering if it would be the right thing to let her go.

So, has anyone experienced anything like this?