Am I Tripping?

As of recently, my bf went out with his cousin and a classmate.. But they were out until almost 4 am.. Fast forward.. He asked his cousin for a girls' number along with a guy number that was also classmate of his. We've talked about this girl before because she randomly messaged him saying "i see you" in regards to a fb post, then she followed up saying "i don't want you to get in trouble for speaking to me" .. he then told her it was nothing to worry about. so after looking in his phone and finding out that he asked his cousin for this females' number, we got into an argument. he told me he asked for the number just to have in his phone.. my question is.. what guy gets a womans' phone number just to have in his phone while in a relationship? he says i'm "doing too much", "i shouldn't have been looking in his phone" and "i should trust him.. am i tripping? am i wrong? what's the thoughts on this?

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