Finding it hard to trust my boyfriend?

I've been together with my boyfriend for about 10 months in total, but only 5 months officially in a relationship, before it was just casually dating. I recently found out though that he was still in contact, and still seeing girls he had slept with in the past. As in, still catching up with them whilst we were in a relationship. He said its because he didn't want to see like a douche by sleeping with them and then cutting ties with them. But i asked him, what about me? What about the fact that whilst in a relationship with me, he was catching up with these girls BECAUSE of the the fact that he'd slept with them. I was so upset with him, and i still am. I dont feel like i can trust him anymore. What should i do? He's away for a family holiday for 2 weeks. I really want to talk to him when he gets back.