It's a good sign he is connecting with males. One of hallmarks of a Nice Guy is their women pleasing, and their drifting away or uncomfortableness with male relationships. This puts a ton of pressure on their female partners, who really are not equipped to replace male friends. And if they're anything like me, they begin to lose touch of the masculinity, and then rely on their female partners to validate their masculinity. They believe they are better than most men because they are not a**holes and are not like the other selfish men. When their behavior doesn't lead to intimate success with women (like me) or their female relationships don't meet their needs they become resentful because they are such good guys. Hanging out with men can help take pressure off of their female partners and can remind the Nice Guy that they're a man, and can have fun being a man. Basically it's the GAL a Nice Guy needs to break his unhealthy relationship with women.
Crappy situations. We nice guys mean well, but we misplace our energy and then become exhausted.
Although I like to hang out with men, and make friends easy and can do the masculine thing, I too withdrew from male activities in service to my wife and her stressful career. The strange thing is that although that seems romantic, it doesn't seem to work, whether it be losing the woman's respect and desire (in my case), or our own masculine identity, confidence, and happiness (like it sounds like happened some of the significant others discussed in this thread).
For whatever it's worth, I believe most Nice Guys have absolutely no idea how destructive their behavior is to themself. That's why the book can be such a tough but necessary eye opener, If they're open to reading it.
One of the difficult thing about the Nice Guy syndrome is that we men, if we were born in the 70s or later, is we were raised to believe that devotion to women was what a modern man should do. Basically, the post feminist movement spurred a generation of men who felt that squashing their masculine energy would lead to utopian partnerships, great relationships with women (after all, don't all women want a nice guy), and would undo the millennial abuse of power men have perpetrated on women.
I totally believe in feminism and believe a lot more work is necessary by men to work on treating women as equals and with respect. But for us Nice Guys, our devotion to our women at the expense of our masculine selves ignores male/female biology. And hurts us and our female partners we love so much. It's a tough lesson to learn.