If you are worried about him losing his erection during sex, bring it up and talk to him about it during a non-sexual time. Just tell him it is something that happens and ask if the two of you could work on figuring out better positions so it doesn't happen.
What man wouldn't like his wife asking to have more sex to experiment with positions?
I, for one, can't handle how it feels when air gets in. It just hurts to me. For us it usually happens when I am on my knees or we change positions in the middle of a romp. If he is pulling out all the way and really isn't noticing, it may be as simple as you changing the angle of your hips.