Would you believe him

I went through the car today and found a open pack of condoms, one used . When i confronted him about it he told me he bought them when i told him we shoukd atart using condoms but we never did, the one gone is from his brother, he claima that the reason they are still there is because he thought his brother took the whole box and not just one. I mean the story makes since but if the story is true i wonder why he would even keep them once he saw i didnt make him use them. Apart of me believes him but apart me thinks im letting him get me with a lie