>>1 "see my friends wiht someone else" in what way? Romantically, friendshippy ways, etc.?
If you mean romantically, then, well, you need to back off a step or two and give your friend(s) some space. Aside from friendship, some people seek romance, too.
If you mean in the friendship manner, then you're possessive. Possibly because you're afraid of being replaced, or because you reject the new addition to your friend's circle. Being opposed but not being able to speak about it, so to .. well, speak.
In that case, you should put down your ego and try to see why your friends enjoy hanging out with that "someone else". If your friends, you must share some similarities or common interests. What are the odds that this new addition will share similar interests with you?