Tmi nipple simulation during sex....

So I'm not with my baby's dad, and moved back home to be with family. Long story short my fwb of six years and I started going up again a couple months ago. I'm 34weeks and when we have sex he's been sicking on my nips a lot , way more than ever before. And I've noticed when I press on them some liquid is coming out. Do you think he's getting colestrum out of my boobs? I know weird question.... But I'm wandering if that's why he's doing it so much ?!? I'm going to ask him next time but any ones partner do this?