I betrayed my boyfriend's trust, how can I make it up to him?

I've been in the same situation, but with a different outcome. It seems to me like your boyfriend loves you until he finds someone better, which isn't a good thing. This is something that you need to think about. It was wrong of you to test him like this, but it was also wrong of him to become interested in another girl. I think the best thing for you two to do is take some time apart and think about things. That way, you two can see what it's like without each other and figure out if you're going to work through this.