I love my wife dearly but I have to specifically remember to think about those little things like texting her little heart symbols for no reason out of the blue. It's like I understand the concept, I just have to specifically think about it and remember "oh yeah, I should show some outward signs of affection because that means a lot to her" just like she has learned "when he gets home from work, he will want to go be alone for a while without any demands until he can re-charge from having to deal with work all day."
I do tell her I love her and hug and cuddle normally when we are together, because she is there with me and so that script is running in my mind. But when I'm at work, or traveling on business, it's a different script that's running and I am not thinking about her then, unless something causes me to do so.
So it's not that he doesn't love you, it's just that there is no automatic trigger telling his mind "I should text her" unless he consciously thinks about it.
About telling him: many people are very resistant to being told things like that. The first thought that would come into my mind would be "Oh great, so now there's something wrong with me and she's going to want me to change how I act" which is, sadly, one of our challenges - it's hard for us to change some behaviors. Just like if I were to ask you to suppress all of your emotions and think purely logically, ALL of the time. How exhausting would that be, and how difficult to stick to it?
But, if he is having other challenges in his life, and can't seem to figure out why he has problems with things that others find easy, then he might welcome the idea that maybe he should look into AS as a possible explanation.
There's an old joke: how many psychologists does it take to change a light bulb? Only one, but the light bulb has to really want to change.
So if he's happy with how he is, he may be less receptive to a direct approach. You may have to help him discover it for himself.