How do I keep from not stressing out when he’s not texting me?

I would make the argument that it is actually healthy that you aren't always texting constantly. There's a level of autonomy necessary for people to maintain and grow a successful relationship; not every element of your lives should be shared with each other. I don't like the term "clingy" due to its inherent negative connotations, but I will say that the need for constant communication usually leads to people smothering their partners. It's not necessarily healthy for any relationship -- romantic or otherwise. Consider the future you want with this person and try to make peace with the fact that there will occasionally be some dead noise.

But are you stressed because you're afraid he's sleeping in and late for work? Or ignoring you? The two of you are together for a reason, and you can mention to him you would love to hear a good morning from him. It's normal to worry depending on the situation. I don't know WHY you're worries. If it's for no reason, you're not a morning person, etc, try to talk it out. All the best etc.

I've been through this too and I know it really sucks. The first step is to figure out WHY you feel stressed. You already know his reason for not texting back, so why are you worried? Could it be you're afraid that he may not want to talk to you, or that he's talking to other girls? If you knew for SURE he was sleeping or at work, you wouldn't be anxious, right? I think you should work on building trust. Have you tried talking to him about it? Maybe he can help reassure you and come up with a way to be more relaxed about your communication. I hope this helps at least a little bit. Good luck!!!

You understand that he has work and sleeps late, so you're not worried about him cheating - or at least, you shouldn't be. Remember that his phone could be off, and also keep in mind that people aren't constantly on their phone. You need to figure out why you're getting stressed. This is the only way you can stop feeling stressed.