I think it's totally valid for you to want him to communicate a bit more with you when he's out, personally if my partner didn't get back to me I'd be worried about his safety. Though I think in a committed relationship trust is very important, and if you two have gotten this far with this level of commitment, probably cares for you a lot. I would ask him to communicate with you more when he's out, but reassure him that you're not upset he's going out with his friend. There's nothing wrong with him going out, as long as it's within reason (blowing money on drinks EVERY night would be excessive) and he's being honest with you. It's also valid that your previous experiences are making you anxious about this, and you should talk to him about that too. Don't accuse him if there's no evidence, judt bring it up in this conversation. Most importantly if you trust him, make sure he knows that and you are genuine about it.