Anyone else?

So my boyfriend has this weird thing about cum. It’s actually quite weird because I’m not a very gross person when it comes down to body fluids but I’m not sure if it’s a him thing or he does it for another reason but,

When I give him head, if we do it as foreplay and he doesn’t cum he’ll kiss me and nbd. But if he cums and I swallow he’ll kinda brush me off.

It doesn’t bother me it just makes me feel a bit... curious and weird.