Okay, this is going to sound strange as well, but if your bf is stimulating the lactating process just be careful that he doesn´t make a sucking motion directly on your nipples, because that will cause them to clog and ultimately dry up. When a baby is nursing, you´ll find that he/she moves the jaw up and down while holding its mouth around the nipple, and that´s the movement you want to stimulate lactation. So it´s actually very different from drinking from a bottle or sucking from a straw.
Not sure if I explained that correctly, hope it helps.