Hey Wlesh, did you speak to him?
Sounds to me like he is up to something, even if he didn't cheat on you that night it doesn't sound like it will be long before he does. I'm with 4get in that I think you know when your fella is capable of it or not. When my man goes out with his friends, sometimes he won't be back until 4am but I trust him completely, and I know he the same with me.
I've never felt the need to check my fella's phone, but I know that he doesn't have a problem even if I did because often I'll faff around on it (it's btter than mine!) and play games and stuff, and if he is out of the room I will answer it, etc, and he does the same with me.
I do think that whatever your bloke was up to that night, he didn't want to be disturbed.
And just because I am nosy and want to get a better idea about him - what was he texting his ex about?