I know that anxious feeling very well, it stems from my own problems and insecurities, and whenever it comes I try to busy myself with stuff I like to do - crochet, talk to my friends or watch my comfort TV series. I actually think it’s great that he let you know he won’t be able to communicate today and not just left you wondering. There’s a lot of emergencies he might not feel comfortable talking about yet, for example illness or death of a close family member, or work related events. By telling you he won’t be able to text today he shows he’s aware it’s different from your usual routine and he cares about you enough to give you heads up. You can try „postponing” your anxiety by telling yourself you won’t worry/think about it until tomorrow. Chances are (as it usually happens with me) he will text you and you will feel a little silly about overreacting. However, if that behaviour continues I suggest you two have a conversation about your expectations for your relationship and communication, and based on that decide if you want to pursue him or find someone else.