Jealousy and do you think to be jealous over this situation was right?

Heyyy 

My girlfriend went yesterday with on of her female fiends (she doesn’t habe male friends) to an indoor swimming pool and had fun there. After that i got overwhelmed by jealousy for her having friends and going out with them and especially that she had fun and i wasn’t the reason for her fun. 

I flipped a bit out and wished her friends a painful death and other things. 

In my opinion the partner in a relationship should not be allowed to have any friends or contact outside their partner. 

Do you think I got to jealous over the situation or not jealous enough or do you have your own experience of what made you jealous to share with everyone? Let me know!