If Menelaus did know he would likely be crushed to know, even if he himself wasn't looking to be with anyone right now for Arianna's sake. He didn't want her too attached to someone that may leave. He didn't want her heartbroken.
He nodded, knowing Helen would tell him when she was ready. He wasn't going to force her to do anything. "I know it's painful to think about, but maybe this will be good for you." He didn't want her to think it was over for her, she would be happy again.