Can You Really Teach An "Old Dog" New Tricks?

Can you really teach an old dog something new? I was sure hoping so. Not to call him an "old dog" but I am only implying that he was my partner, my spouse, my other half and we had been together for quite a long time. He and I knew each other so well, or so I thought. He was not a young man, actually he was 40 plus. He was no baby by any means. He should have already gotten his running around over and done with. Now, the other woman was calling him like crazy. He was not answering any of her calls, at least when I checked his phone, they were unanswered. I was hoping for a blessing. Who was I , to think that I could teach him to want to be with only me? I wanted him to learn how to be happy with me, just me and our family, and not turn to anyone else. Was I asking for a miracle here? Yes, to be honest with you, maybe I was reaching a bit too far. I wanted him to learn how to be happy without having someone extra in his life.