"Friendly uncle"? I'm not gonna whip out the "OMG, he's a creepy pedophile!" card (it sounds consensual), but c'mon now.
Anyway, the lying and sneaking around is fucked up. I get that you're afraid of starting a scandal/drama/judgment-fest with your family and friends, but is there anyone who actually knows your husband whom you could confide in? People on the interwebz are mostly just going to react in shock (sounds like maybe you're looking for a harsh wake-up call?). It's hard for someone who doesn't know the history and nuances of your relationship to understand why you'd want to save this marriage, since everything you said in your post makes your husband sound like a colossal sleazebag; the only detail you left out is the white van.
I'm sure you have reasons for wanting to resolve these problems and stay married to him. I'm guessing that either your husband has some good qualities that you've grown attached to and don't expect to find in other relationships, or that this diseased-cum-spewing-dickhead behavior of his is a recent anomaly in what was once a not-so-fucked-up relationship. You didn't mention how long you've been together. Although I have hardly any information to go on (and this is why I hope you can talk to a friend/family member/bartender/whatever who'll give you an honest, informed opinion), I find it astronomically unlikely that any number of sweet memories, inches of penile prowess, or dollars donated to humanitarian causes could outweigh the fact that your husband has lied to you OVER and OVER again.
I don't necessarily believe in things like "once a cheater, always a cheater" (though exceptions to that one seem rare), but this doesn't seem to be a case of someone regretting bad behavior and trying to change it. He clearly doesn't want to change. And seriously, WTF, you're already in an open relationship, and isn't part of that kinda supposed to be about open communication?
(FAIL.)
Anyway, you can do better. At the very least, go explore the open side of your open relationship and get to know some people who are awesome and attractive AND have extra time to spend with you since they're not so busy hitting on their teenage step-nieces and buying them expensive sex toys and then covering their tracks buying you cheap replacement sex toys.