Use the anchor formula: status, reason, return. Status is where the relationship stands ("we're good," "I'm not upset"). Reason is why the distance exists ("work is slammed," "I'm at dinner with my brother"). Return is when contact resumes ("I'll call at 7"). Twenty words, and all three of their open questions are closed.
Short beats long for a reason. A long explanation gives an anxious brain more surface to scan, and over-explaining pattern-matches to guilt. The defensive paragraph you typed to prove everything is fine reads as evidence that something isn't.
Believable beats grand. "I will always love you no matter what" is unfalsifiable, so an activated brain discounts it. "I'm not upset and I'll see you Friday" is checkable, near-term, and concrete. Reassurance lands in proportion to how verifiable it is.
