Anxiety over texts?

So I'm in a relationship that just kind of happened. Neither of us has ever officially asked the other one out, but we're exclusive to each other, exchange I love you's, he refers to me as his girl.

Anyway, we have a fairly large age gap and he's just not into texting, social media, etc. Sometimes he texts me a lot and sometimes he'll go hours without responding. He's a busy guy with work and his kid and that's fine, I understand. I know some people will say "he can make the time if he wants to" but this is how he's been since I met him (we were best friends before), it's just him as a person, it's never changed.

I have no reason to be suspicious or jealous of anything either. But sometimes his lack of response makes me anxious (that might not be the right word but I can't explain it really.) We only see each other like once a week because of our work schedules and I'm back in school and..well I miss him. When were together its like the whole world stops, what can I say, I'm in love.

He had a pretty traumatic childhood and relationship he got out of before we got together, so we're working on affection and lately he's shown some really good progress and said some really sweet and meaningful things. I look forward to those conversations and I miss them on days like today when he's not been very responsive.

I know that he's mine and I'm his and that he loves me and I don't doubt any of that for a second. But how can I work on this anxiety?