I know there are plenty of reasons I shouldn't. I still want to ask anyway. I mean, he knows where I live; I don't feel his living situation should be a secret.
Go over all those reasons you say you know are why you shouldn't ask until they sink in. This "I still want to ask anyway" tosses away all the valid reasons to not so pursue - you give the reason that "he knows where I live; I don't feel his living situation should be a secret", and that doesn't strike me as a significant enough basis. The real basis, I think, is to have the address so that you can contact him regarding business matters. Your reason just strikes me as
1. You still tying into him; it's an emotional connection you have with what was, that you wish to keep hold on, by knowing what his life now consists of, as he's now a stranger to you, and you're not privy to his goings on as you once were;
2. A matter of your curiosity, as you want to find out if he's living with the OW or not.
I'm not saying that it's a matter of whether you should or shouldn't have his address (personally I think you should, as it serves a practical purpose in contacting him forward going), I'm just observing that the reason why you feel that way may be something for you to reflect on and deem whether this is the path for you to stay on for your healing.
You'll get his mailing address eventually in the normal course of events. When my ex had the moving men over, she didn't want me to see their moving instructions lest I catch her new address. Partly that's because she had lied to me about where she was moving to; she had said it was into her girlfriend's house when it was really moving into the OM's apartment. Yet, not too long afterwards, some correspondence needed to be forwarded to her, so I got the mailing address from her anyway.
What my ex said to me at the time of moving out really shocked me. She said she didn't want me to have her address lest I go kill her. My jaw dropped. I've never, ever been violent toward her; I couldn't believe she even could think that of me. Maybe it's because she used to freak at the sight of a spider in the house and I'd have to kill them for her, so she saw me as a cold-blooded murderer of creepy things. But seriously, perhaps it reflected her sense of guilt. But I digress.
who am I fooling here? If H. were interested in working things out, he'd be contacting me and making that clear.
Reading through posts over the past 1½ years or so, I see it's not always made so clear, as in a formal declaration, yet know that if a WAS wishes to return, then if there is no physical obstacle to them returning, neither mountains nor chasms will keep them away, though it's possible the ex mother-in-law's scorn may prove formidable.
Do they permit customers to bring in 2x4s at french bistros? I have to call and check.