It has everything to do with position and how the guy is stroking. If he exits your vagina entirely and goes back in... he's going to push some air in there. If you are bent over, or spread open in some kind of way for too long before he enters...use your kegal muscles to push out right before he penetrates, this will decrease the amount of air that traps.

Queefs are just air in the vagina. Its nothing to do with you. If he doesn't like them, inform him of techniques he can use like...not holding you open for too long before penetrating and getting in and staying in, shallow is fine just not to pull all the way out a bunch.

Using position that create the tightest seal will help as well (legs over his shoulders, etc.) They are awfully embarrasing and you can't help but feel responsible since they are emmiting from YOUR body... but it takes two to cause them. You don't queef when you masturbate I'm sure, nor do you walk around queefing willy nilly... nor does it happen in all positions in sex... work out the ones it does in, and try to work on ways to keep the air from being a factor.