Like Melissa said, being "too loose" is usually not literal. It usually means a girl sleeps around. It's not really literal because having sex actually does not make your vagina loose. A lot of people joke about lots of sex making the vagina loose, but it's not really the case. Having a baby can stretch the vagina, but having sex won't.
The vagina can actually seem tighter or looser depending on how in the mood a woman is. When we're in the mood, our vagina actually gets bigger. It also gets lubricated. That can make it seem loose sometimes, but it's nothing permanent. If a woman tries to have sex when she is not in the mood, she might feel a lot tighter to her partner.
There isn't much you can do to stop air going in and out of the vagina. The only times it has ever happened to me is when I was with a new partner, and we were changing positions a lot.