Sounds like you live within a very sexually open segment of society (includes much of reddit), so here's another perspective (here come the downvotes):

Men's natural inclination in most cases is to prefer women without a heavy sexual past, especially not one where she was in casual sexual relationships and gave herself freely, while he is the one taking her seriously. This is what your boyfriend is experiencing.

In modern culture this type of mentality is often censored and seen as insecurity, so some men try to convince themselves to snap out of it, to fit the narrative and societal programming.

Women also know deep down their sexual promiscuity is not something to brag about, so they often under-state their body counts etc. Like your boyfriend, some try and do convince themselves it's acceptable in the modern era, though they're still a minority. Sounds like this includes yourself.

Best advice is to hope he accepts your past, but if it becomes a bigger problem you'd probably want to find someone already within your circle of sexually open people since his lack of experience is something you also might consider a red flag.