I can see why this is making you nervous. YOu do not know what to believe of his intentions. And if infidelity was one of the problems in your marriage, even more so. But I think you need to look at the big picture here. What evidence do yo have that this is not just a perfectly harmless outing with friends. Evidence beyond your own fears, I mean. You might have chosen not to hang out wiht male friends during this period of uncertainty, but does that mean that if you did happen to go to a movie with one of them that you were sleeping with him....or had any intention to cheat. I doubt it. What you seem most to be upset about is appearances. He is not appearing to abide by the rules of this separation.
So are you sure the rules are clear enough. Are they negotiated between you, so you both feel like you got your say in how things should go.
If the rules are clear and he is, for all intents and purposes, abiding by the letter of the rules, then the rest is just trusting him that he has a pure heart. That exercise might be very beneficial to this period of separation. If you can trust him to go out, and find out that nothing bad happens, then perhaps your trust will grow and grow out of this. consider it an exercise in trust building.
I mean hell, if in the end you find out he has been a bad boy, you can dump him anyhow. all you have spent in the meantime is time and faith. so let him go out to his ball game. Talk to him afterward to find out how it went. try not to get up his nose about it.
And, I think, accept a few invitations yourself to a few harmless outings. Might make you feel a bit more in control and no doubt you could use wiht some benign male attention too.