A.P.
E.,
I had to use a nipple shield with both of my children too. Don't worry! With my daughter who was born about 1 month early, I used it until she was about 6 months, and as her mouth got bigger and stronger at 6 months old, she then gradually got used to nursing without using a nipple shield. With my son, I think I used it for about 2-3 months. And even though my son was born almost full term, both of my children were under 6 lbs when they were born.
For me, E., I was grateful to God that an "invention" as a nipple shield existed because I truly wanted to brestfeed my children. My nipples were flat too, and we had complication with our baby not having enough sugar, etc. So once I found a nipple shield that fits me (the one they gave me from the hospital was still too big for my little ones), I was nursing them with joy! It was a "lifesaver" in my opinion! I just thought I wouldn't be able to breastfeed due to my anatomy, and I cried a lot struggling trying to nurse without the nipple shield because one lactation consultant made me feel really bad that I was using it....and saying that they won't EVER get used to my own breasts if I keep using the nipple shield.
Well, E., the lactation consultant was wrong, and in due time (when the baby is ready), they will get strong enough to latch onto you directly to nurse without the shields. So please don't worry how "long" it'll take for them to nurse without them. Just enjoy the time nursing your baby, and when your son is ready to latch onto you directly, he'll do it. And NO, your nipples won't get messed up! (hee-hee!) In fact, the nipple shield helped my nipples get elongated (as they should with nursing), so when my babies were ready, breastfeeding directly was an ease.
Sometimes, I think lactation consultants can be pushy about breastfeeding without any aid. But if that's what it takes to feed your baby, I say go ahead! I listened to myself, and I only cared that my babies were getting fed and gaining weight, and I stopped caring about how the breast milk was getting to them.
I hope my response helps! Hang in there and really enjoy your breastfeeding sessions with your little one. That YOUR very special moment with him.