What this boils down to is that you dont trust him SD and that in itself is very dangerous because you want a commitment with this guy! When you split last time, he tried it on with his ex didnt he? Has he ever cheated on any of his previous gf's? Just trying to get a handle on why you dont trust him... Whether there is grounds for it or just your own insecurity from someone else.
AND Yes it's hard to take the fact that he wants to hang with his mates who are purely out there for the chase but he needs to go down that path himself...once there I'm betting he will actually be quite bored with the whole thing and want to come back home early...to you!
I dont think that you should guilt trip him into not going even though that may be a hard thing to except.
On the other hand you could also go out with your friends for the exact same reason as he is...he is a Libran and now he will feel how you are feeling...