In my opinion, do NOT tell him what to do!!
However, since it's only been a couple of months, I would certainly tell him that you're NOT good with him going to do this.
You can't control what he does, however you can sit back and watch what he does.
If he's truly putting the work in, and showing that he can be a safe partner, than he'll realize your feelings Trump his cousins or what he wants to do in this situation.
Reconciliation isn't just done by words. Nope!! It's done by one action at a time, and if he chooses to go (and it doesn't matter that his dad will be there) he's flat out showing you that it's about him and what he wants.
So it's a bachelor party.....so freaking what. Fact of the matter, it's only been a couple of months, and it's WAY too early for him to be traveling ANYWHERE for crying out loud.
Think about what's going to go on in your head the entire time he's there. It doesn't matter if he checks in. There will be drinking, partying, more than likely strippers and other women, they'll go out partying as well, and there certainly WILL be opportunities to do something that could blow up this "attempt" at reconciliation.
He feels smothered or you don't "trust him"??? Says the guy who has NO reason to be trusted and the guy who knows what a burner phone is and how to use it.
Again, sit him down, tell him very calmly that you're very uncomfortable with him going.
Listen, when your freaking spouse LIES to you (to your face--countless times), CHEATS on you with another woman, uses a burner phone, trickle truths to you as well.....that person, due to their OWN ACTIONS, have put themselves on an EXTREMELY short leash of trust, and thus he either gets this or he doesn't.
"But I'll miss my cousins bachelor party". BOO FREAKING WHO!!! Should have thought about that when you stuck your dick in another woman!!
Let him decide what he's going to do after you've told him you're not comfortable with this.
Do NOT do it in a passive aggressive way!!!
Tell him how you feel, but you will not tell him what to do. He's a grown ass man and he can decide.
Then sit back and watch.
Is his cousin and a party more important than his wife, who he STABBED in the back, and he's sincerely trying to show her he understands what he's done and he's committed to doing whatever is necessary to rebuild the trust that he DESTROYED and to put another building block for you to see that he's ALL IN to not just talking about being a safe partner but actually SHOWING you.
Just because you're attempting reconciliation doesn't mean it's going to work.
He decides to go.....let him go!! Do NOT pout, cry, get angry, try to reason with him, negotiate with him, etc etc.
LET HIM GO!!
When he's gone, and he calls to check in, do NOT answer the call. He made his choice. Your feelings were secondary. You now going to play small talk with this guy as he tries to tell you how innocent things are up there??
The bachelor party and the trip isn't the issue.
It's whether or not he chooses to go, and he has FREE VOLITION to decide on his own, and he either sees the big picture or he doesn't and it's NOT up to you to show him or convince him.
He decides to go, chalk it up that he's NOT all in, and it will be another example that he is NOT a safe partner.