wow..it seems that when we men ask for advice all we get is more grief. Instead of scolding, berating, and driving guilt down this guys throat (he already said he's not the cheating kind), more practical advice would have been this: have some balls and change regular social plans. Life has already changed due to the baby. Use this situation of the newborn to express a change in plans. People, even relatives, should understand this. It avoids direct confrontation (because not all situations can be resolved this way..that is reality). And this allows your priorities to stay straight (i.e. supporting wife and child, etc)
As for testoterone, man, I appreciate that situation so much. It seems we men are continually being downgraded to animal status when we discuss our own testosterone driven issues that we are truly trying to keep at bay. The last thing we need is to berated for our instinctual drives. Instead, we as men should understand a woman's point of view from their standpoint (not hard to do) and also meet our own needs intelligently (which are not selfish, just human impulses). The smartest choice we have as men is support each other. And when we can't find support, just re-focus and ask ourselves what our priorities are and honor them. For momentary lapses, we must have a personal arsenal of defenses at the ready (mental, emotional, physical..) Or use these impulses to deepen intimacy between husband and wife. There are other ways to celebrate physical love between man and wife so that both are pleased and happy. This is just smart living.