When you tell your bf or gf to not hangout with a certain person is that controlling?

Yes it is controlling. Your bf or gf has the right to hang out around whoever they want to. It is there choice to decide if they want to ruin the relationship. If you have a specific person you don't want them to be around, you could say, " I suggest not to hang out with ___, because they are not the type of person that you want around."

I hope this helps your question. Have a great day!