Most Helpful Guy
You were betrayed and he acted as if his feelings for you were insignificant. I get it!
Most Helpful Girl
If you gave them consent, you have no right to be angry. I'm sorry, but that's the truth. Once you tell somebody that you're okay with their relationship, you can't change your mind nor have much of an opinion about it. You can have your feelings, but you can't say what they should or shouldn't have done since you never told either of them that: "You would be more comfortable if they waited until the breakup was more along." Your boyfriend was clearly on the rebound and didn't take your relationship seriously, but that is normal for 18 and under relationships. It's all new and less meaningful when you're that immature.