If guy pulls out then after a few minutes puts it back in,does the chances of the sperm getting you pregnant go down?does air make sperm less fertile?

No: Sperm can actually live outside of the body for a period of time. That is why ejaculation near the vaginal opening without actual intercourse can indeed cause a pregnancy. Besides that, there is probably some post ejaculate remaining and I would say you are still at risk of pregnancy. If you do not want to get pregnant you should use a more reliable form of contraception.