Dude, DON'T tell her, seroiusly, if it DOES blow up in your face, then the damage is really irrepairable....and then you've got family involved, and it's your sister in law or whatever.....nah nah.....it would be one thing if it was just friends or something, but not family, trust me on this. Your wife knows that you're so into it? I'm a bit surprised she hasn't given you hell UNTIL now! I know all the girlfriends I've ever had that I've told about it get REALLY pissed and jealous when they've seen me (on, like 2 or 3 occasions) tickle another girl.
Seriously, we gotta know when to quit while we're ahead! I know it's painful, especially when you see those opportunities.....and yeah, it makes it harder when the woman is asking you point blank why you're not playing around anymore.....but that doesn't necessearily mean she's "into it" and your saying "you wouldn't understand" is dead-on accurate, probably. Hopefully it's not a cryptic enough statement to give her some thought! But really.....I would hate to see something blow up in your life over this.....what would happen if your wife started hunting around your internet activity, oh man......I actually had an uncle who tickled my girlfriends, and my brother's girlfriends.....and it was NOT appreciated, by the girls, nor by my brother (nor by me, actually!) and it eventually made a HUGE stink that to this day, years later, still has not been totally resolved (and I don't necessarily think he's one of "us").....so.......to the Great Toyou, he who has given us so much and asked so little....our brother, and friend......I know it's hard, but just grit that teeth, and be happy with the great times you've been able to have in the past, and on here, and you know.....you'll still have your opportunities! But getting older DOES mean less opportunities, unfortunately. It sure ain't like it was when we were in college!
Good luck, brother! I feel your pain!!!