Ron really did feel bad that he had never told his wife. There just hadn't been time what with the war and everything, and then they had gotten married, and they had already had sex by that time so it just wasn't as important. Ron just didn't think about it much after that, and it wasn't that it had slipped his mind, it just wasn't part of his daily thoughts.
"I was sixteen, and Lavender and I were together and you were pissed off at me anyway. And it just never came up. We didn't talk about it." He shrugged and looked a bit sheepish. "We were just busy, and by the time we got married we had been together for some time and there just wasn't a chance to bring it up."