Leaking milk during sex

Hi, I am 26 weeks and my boobs size increase from 34B to 36C. My partner is so happy to see growth, he likes to fondle the breast and suck my nipples during sex. He got excited when there is milk leaking… and I orgasm and follow a few more. I am experiencing a spike in my libido, and I am enjoying sex more than before pregnancy. Is the breast off limit during pregnancy? I heard that nipples simulation may cause premature delivery.I want to continue enjoying sex. Please share your experiences.