As someone else said, the real answer is that this is a comic.
We don’t really know from the OP whether they have been together for an hour, day, week, month, or even year (and he just never found the hoodies box yet?). Irl women are stigmatized with “slut shaming” for having multiple partners, and while men get stigmatized too this is not one of those ways. So irl she might have kept it from him until she was sure that he was mature enough to handle the truth. Although she could have also used it as a test - if he were a toxic masculinity believer, better for her to know the truth right away and get far away from him?
So there’s deep stuff contextually related to this… but this is a newspaper comic community, so it is unclear how deep most people really wanted to get into the deep analysis of its backstory, unlike e.g. political memes where that is more the point.
As someone else said, the real answer is that this is a comic.
We don’t really know from the OP whether they have been together for an hour, day, week, month, or even year (and he just never found the hoodies box yet?). Irl women are stigmatized with “slut shaming” for having multiple partners, and while men get stigmatized too this is not one of those ways. So irl she might have kept it from him until she was sure that he was mature enough to handle the truth. Although she could have also used it as a test - if he were a toxic masculinity believer, better for her to know the truth right away and get far away from him?
So there’s deep stuff contextually related to this… but this is a newspaper comic community, so it is unclear how deep most people really wanted to get into the deep analysis of its backstory, unlike e.g. political memes where that is more the point.
Oh ah… I mean, b/c hers is bigger than his. :-P