When my daughter was an infant, I belonged to a "Parents as Teachers" group through the local school district. We had a speaker once who told us that parents shouldn't say "I miss you" to their child because it puts the responsibility for being "away" on the child and can cause feelings of guilt. Instead, the parent should say "I love you". That seemed reasonable to me so I never said "I miss you.". Years later (just recently), I was having a conversation with my 12 year old daughter about her going away to Girl Scout camp when she said "You never tell me you miss me when I go away to camp". First, I was shocked she noticed that at all. Second, I explained why I never said I missed her when she went away - I didn't want her to feel bad about being away and having some fun away from mom and dad, but that I always tried to remind her how much I loved her. I didn't want her to feel guilty and that I thought me saying "I miss you" would make her feel bad about not being home. I told her that of course I missed her -- madly -- every time she went away. She got a huge smile on her face and gave me a big hug. She understood and it made her feel even more special that I was so conscientious about my choice of words to her.
It seems your son only wants to express the obvious, he wants his daddy home. If we feel guilty about the words our kids use, well, that's what being a grown up is all about. Your husband can either change the situation, or just try to make the best of it. Asking your son not to say it is, again, putting the responsibility for the situation on your child, which is all kinds of wrong.
Now, my son says "I missed you" all the time, even when I'm gone only long enough to pick up dinner. He's funny that way. I'll say "I missed you too", but never first. I still say "I love you".
After my conversation with my daughter, I don't know if the speaker at the "Parents as Teachers" meeting was right or not. I mean, if my daughter was so acutely aware that I never told her I missed her, what might have changed if I had? I do know that letting our kids express their feelings, no matter what level of guilt that puts on us, is what will keep the communication lines open for as long as possible. And believe me when I say you and your husband will miss it soon enough when your son doesn't say "I miss you" anymore.
Blessings,
N.