I find it sad that anyone should feel guilty over doing something which is so utterly human and common. I fear, it's most likely, as one reader stated in yesterday's comments: this brother only feels guilty because his wife is now aware of it; that it's not guilt he is experiencing, it's embarrassment, it's shame.
Married, heterosexual men aren't supposed to be jacking off - they're supposed to be having intercourse with their spouses. If heterosexual men do it at all, they certainly aren't supposed to whack the willy with other guys. They're supposed to pretend they never masturbate at all. Ever.
It's like being ashamed you get boners.
Which is hogwash. A man should never be ashamed of getting an erection.
Solo sex - even when in the presence of other men - is extremely common.
Yes, even for self-identifying heterosexual guys.
Jack Off groups around the country are proof of that; they report that 25% of the guys are straight men who simply enjoy getting together with other males to engage in a very common activity. They report a strong sense of brotherhood.
Dude, I hope you shed those emotions. Go back to enjoying time with your brother when the mood strikes you - without guilt - particularly when your spouses are okay with it.