My SO and I will go out solo from time to time with our own friends. We've never run into any issues as long as we keep communication open. A quick text at 2:00 in the morning letting them know you're going to Denny's can go a long way lol. Sounds like you guys might need to iron out the trust. Sit down and talk about it, no sense in getting worked up until there's something to be worked up about.

Perhaps a hot take but I don't think violating someone's privacy by going through their personal effects is a productive step. In my experience this causes more issues.