Been there, had the badge and worn the t-shirt as they say at the end of 1986 start of 1987. No mobile phones or internet at that time. I look back and wish i'd been stronger! Today I would say to you that once the trust has gone that's the end. You'll drive yourself crazy when he goes out wondering where he's actually gone, who's he phoning, what's going on at work. If I'd have heard that part of the conversation about leaving after the holiday I couldn't have kept quiet. I trusted my ex and never in a million years would have thought he was capable of what he did. I knew something was going on but didn't want to believe it. Have you asked any of your friends if they know what's going on. I found out that mine did but didn't want to tell me just in case he came back and I'd never know. He never came back. Would I have had him back? Yes at that time I would have because I loved him so much. My brother did the detective work without me knowing.He found his car, just a couple of mile away from me. She worked with him too.
I'm just wondering if someone could put a camera in the flat? Other than that I would ring the number you have or ask a friend to. Ask to speak to (husbands name) and go from there. Or drive to the flat and sit outside close by and see who he goes in and out with. Easier still, confront him with the phone bill. I hate to have to say it but I think the affair's still going on. Once a cheat, always a cheat I'm afraid and as I said, once the trust has gone you'll never believe a word he says again. Do keep in touch. 
Patricia Greene who played Jill Archer has died

