They lock their phones, they start leaving the room to have private conversations when the phone rings, they take their phone everywhere even to the bathroom. They shave and shower before going somewhere where they normally wouldn't bother. I have long hair and I find it everywhere even on my car seat, if he has a lady friend with long hair- You will probably find them. Lateness, his phone turned off and no text back when You know he should not be busy, excuses to spend time away, showing heaps less interest in You, and not wanting much sex any more. These are what my friend and I came up with when discussing catching her ex out. She found long black ex girlfriend hair down the shower plug hole and checked the bins. Sure enough the lady had thrown small items of rubbish in the bins. Oh nd check all computer history, bank.statements, credit cards etc. Look for any random repeat numbers or repeat expenses as well as the obvious reciepts for flowers and hotels. Get a teenager to hack into his laptop if You are sure but just need proof.
He is probably flipping out over very simple things and looking for any reason to be mad at you. Maybe, I'm not sure