You are handling this right, blue:
Encouraging him to go was the right call. NOT phoning/texting him in a way that screams "I'm checking up on you" is the right call; let him call or text you if he feels like it. Showing him complete trust is very important, because there are few things that piss a person off more than feeling like their significant other is projecting baggage from previous relationships onto them. I've been there, and have dropped the girl like a hot potato...and I've sure to express to them "I'll be goddamned if I'm going to pay for somebody else's mistakes" on my way out.
Stay the course, and when he gets back, resist the urge to interrogate; do not demand a complete de-briefing with every detail of every hour of his time away. A simple "how was it?" and "did you have fun?" will suffice.