Hi OP,
This is obviously really stressing you out but it'll be okay, just try to calm down a little bit. I doubt he was with anyone else. It could be anything from he left his phone in the car, was sidetracked with something else, phone ran out of charge and he couldn't find his charger, he fell asleep early (I get up at 5.30am for the gym and feel sleepy at about 7pm!). Also, if he's anything like me, sometimes I just take a break from my phone for a bit. I'm on social media a lot but sometimes I just need some down time. Plus he text you first thing, so that's a good thing!
It will obviously help you to know where you stand with him so I suggest working on that. Next time you meet, just casually ask him about being exclusive. Mention that you'd like to be and see what he thinks. It's fine to ask, in fact, it's an adult and sensible thing to do! If he's not up for that at this point, you can then decide if you feel like you can proceed with the relationship. I would say it's fairly normal for him to still be on Tinder at the moment, it's only been a month, but if you have the exclusivity talk, he should have no problem deleting it.
Please don't text him accusing him of anything. I have terrible anxiety and I know how easy it is to jump from 0-100 but the likely explanation is probably completely innocent.
If you do want to keep the relationship going (and at the moment I'm not sure if it's the best for you) then please speak to your GP about possible counselling or help for your anxiety in this area. I mean this in the nicest way possible. This behaviour is not healthy for anyone in the relationship and will only serve to destroy and it will always become a self-fulfilling prophecy. This comes from someone who used to have awful issues with being away from my partner for any length of time (picture breakdowns, crying, panic attacks) and it is something you can come to work through. I've gone from that to having a partner who forgets to text me for hours because he's useless and I'm totally okay with that and trust him entirely. Your relationships will be much healthier as a result of counselling / help and, most importantly, you will feel healthier, more confident and more independent.