So did you tell him that you woke up at 12 and he wasn't there?
Why don't you feel that you can speak to him?
There has to be more to this than what you have put. Have you been having problems?
My marriage hasn't been all roses. We even split and nearly divorced. There have been times I didn't feel I could speak to dh about how I felt. There was nothing in particular just grown apart.
Now, we always talk. It's not always easy. And it hasn't been easy to get to this part. But we talk. No matter how bonkers what we have to say is.
6 years ago I wouldn't have wanted to get into with dh as I wouldn't feel listened to.
Now, I know if I had suspicions or dh told me something that didn't add up, I could say 'well why when I woke at midnight why weren't you here?'.
If he is up to no good, but has a plausible explanation, he will be probably be more careful for a couple of weeks. But then revert to his behaviour. At which point you can reassess what you want to do, do you want to check his phone without him knowing etc.
The fact that you can't tell him straight up that you know he left before midnight suggests to me there is more to this. It's not just what you have put in your OP.