Fear of Rejection
On the surface level, it's not uncommon for a guy to worry about—and resent—the shift in his partner's attention from him to the baby. From the early stages of pregnancy, guys slowly begin losing their sole claim on the partner's body, which isn't something they happily give up. The lack of sex in pregnancy and childbirth relates to rejection because one of the most powerful ways men feel acceptance is through sex. Conversely, then, there are few stronger signals of rejection to men than "Not now, honey." Even when guys know they can't expect a favorable response, they'll still feel hurt when they don't get one. It's a tough adjustment.