My best friend got together with my best friend

I'm supposed to be happy that my male best friend got together with my female best friend. I know them both for over 10 years.
They were there for me (separately) during my break up many years ago after a long period of non-contact.
I'm closer to the guy than the girl all these years. Recently they got together.
Maybe they weren't clear so they didn't tell me earlier, but I guessed it. But the way they denied it made me feel like I was imagining things. 
They told me a few days ago, but all I felt was that I don't want to know anything. And I don't want to meet them anymore. Together or separately.
I feel like I just lost both my best friends. I feel like my best friend stole my best friend from me. But I feel happy for them. They deserve to be happy. This is their first relationship after all.
I just feel confused. Maybe a bit jealous. Like I'm the only one single left.