Condoms Breaking

So my partner and I are very rigorous about protected sex. I'm on the pill, he always pulls out, and we use condoms because I'm not about to be a teen baby mama when my dreams are Ivy League. Unfortunately we're both also super new to the whole sex thing and our condoms keep freaking breaking. The last two days we had sex twice and it completely split and peeled back both times. Luckily, the first time I'd pulled off before he came and the second we noticed before he finished. He doesn't remember exactly what brand he bought- some kind of Trojan ultra thin, it was the least expensive. The box was less than two weeks old, and we left room in the tip. Any ideas why they did that and any suggestions for what kind to use next time?