Op: the fact that you stated you're going through a moral dilemna means part of you feels guilty because you know what you did was wrong, you felt guilt as you returned to the game and regardless of what people on this thread have said so far, it is an invasion of privacy - the minimum provisions from a legal standpoint does not require the person who's privacy you invaded, to actually be aware that you have done so. The other part of you, acted on the guilty pleasure, with the rationale and justification that no one will find out, no one will get hurt and I won't get caught. And you do this, even though you know it is morally wrong. This polar opposite sides of you creates this conflict.
Has any of us crossed this "moral" boundary? The fact that you're asking this on an escort review board is a bit of an irony because many of us who visit escorts cross moral boundaries already - although there are some of us who are single/divorced/widowed/other reasons where this statement doesn't apply. Some of us are just pure hobbyists, some of us have deeper issues and are using sex to medicate those pain... and yes, it is not a far stretch that some of us have far crossed the moral boundaries of acting on sexual desires that many would call immoral.
While many others are focusing on the fact that you went into your friend's master bathroom, or invading your friend's wife's privacy, and less so about you relieving yourself, I believe the focus should be the opposite... or rather on the fact that the bra turned you on in the first place and the fact that you chose to relieve yourself. This is indicative of a developing sexual behavioural pattern that is unhealthy and can be damaging to your personal life. Ask yourself this. Why do you think it turned you on? Did it make you feel powerful? Make you feel good about yourself? Maybe the fact that alone that your friend's wife has no idea of this makes you feel dominating? Did this entire event make you realize this has given you a much more higher sense of arousal than other forms of sexual acts (like normal sex)? Did you find yourself helpless and felt like you had no choice? Would it have bothered you had you not act on it? There's obviously some deeper questions or issues at hand here.
The fact that you chose to cross the boundary to relieve yourself, pretty much disallows you to reason this whole thing as plainly just a fetish or a kink - or we're just being men. So as much as you want to lie to yourself and justify your actions, or write it off as it's no big deal, there's likely some deeper problems that you have - something to really consider about. Hence, the reason you have guilt in the first place. If this was purely just a fetish or just men being men, you wouldn't have harboured those feelings of guilt in the first place.
Of course, this is all speculation as I don't know anything about you (the op) or about your history or anything else. But hey, you asked for some advise and perspectives, here it is.