Is anyone in a relationship but still happens to get jealous when other friends get in one themselves?

I've had a long lasting relationship for about four years now.. and I'm grateful and appreciative of my boyfriend. But I've noticed lately that I've gotten really jealous of new relationships my friends seem to have. A very close guy friend of mine just got with one of my other friends. I never knew they were actually going to turn up being boyfriend and girlfriend.. and now things are just awkward because I don't feel like I can trust him knowing that he has someone else he has to be close with. And also.. whenever I hear people are getting together..I have the tendency to criticize.. harshly. It's like I want everyone alone, except me, it's hypocritical. Does anyone else feel this way?