Is it normal that my boyfriend wants to try dating other girls?

My boyfriend and I started dating when we were 14 and 15. Now we're 17 and 18. There have been three encounters with other girls. All of them are from his work. What happened with all of them is that he wanted to go hang out with them at their houses, but never ended up doing so. Last weekend, he asked this girl to dinner. When I found out, I broke up with him because it was the third time he's taken interest in other girls and I didn't want to deal with it. There's been other problems too. I couldn't handle the pain of him wanting someone else. Now that we're broken up, he's been trying for two weeks to get back together with me saying that he doesn't want any other girl. He's said that every time after he wanted to date someone else. He'd see how much I didn't like it and that I was thinking about leaving, then he'd change his mind and say that he doesn't want anyone but me and was just confused and knows now what he wants. What is on his mind? Do you think I should get back together with him? I told him he should go explore then maybe we can get back together.