My baby is 9 months and all of a sudden he will not go into his crib. is this separation anxiety? if so what do i do?

Probably: It's a pretty typical age for this type of problem if that's what it is. If so, you can put him in his crib, then sit next to his crib until he's asleep. Then repeat the next night, but a little farther away. And so on until you're out fo the room. That way you're still with him and you don't traumatize him too much. But be strong; once he's in the crib he stays there.