gagging on his dick? πŸ˜•πŸ˜•

Destiny
So I found out resently that my boyfriend likes gagging for some reason, even tho his only reason to my question of why is "I just like it" πŸ™„. Through the course of our relationship I have always tried not to gag because I absolutely hate the feeling. But I want to give him that pleasure. I just don't know how. How can I make myself gag?? 
PS I've tried faking but it doesn't  work.