Annie, beautifully stated.
^^ diddo .. I have been breastfeeding for 14 months and it's much better than I thought and so much easier. But if it's not for than its not. It feels weird in a way when you first start unless you have an open mind set about it.
Taking your boyfriend out of the equation for a minute, looking at just the nursing part -- my sister in law was the only woman I've ever known who tried nursing and didn't like it. Once you talk to the lactation consultant or take a nursing class at the hospital, you will feel a lot better prepared and will know more of what to expect. (I think my sil didn't have the advantage of a lactation specialist to talk to; she had her first child abroad and then gave up on nursing altogether.)
Anyway, it is not scary, you don't feel like you're being squeezed or sucked (it's not like the kind of mouth/breast stuff your boyfriend might do). In fact, you don't feel the milk being sucked out (though if it is being sucked out when your breasts are too full you feel a blissful relief of pressure, a tiny bit similar to the way your bladder feels as it goes down when you pee). But you don't feel it like you are thinking based on your boyfriend's mouth.
The nice thing about breastfeeding is how simple and clean it is. You take a couple of breast pads along and a wipey for your breast afterward (if you feel you need it -- breast milk is sterile and wonderfully resistant to bacteria, so you really don't) and you are all set to feed your baby. This compared to bottles, which you do have to sterilize, and fill, and keep warm or cool, and tote around, and wash, and remember to have, and hassle over. Breastfeeding can be such a breeze compared to that. There is also a wonderful bond with the baby, who usually keeps his or her eye on you when drinking, and sometimes tucks his little hand up under your armpit or around your back. It's pretty blissful to feel that close to someone.
As for your fiance, please just tell him to put a sock into it for now. As I said in your other post about this, if he is doing it because he is developing some kind of erotic fantasy involving spurting breast milk, tell him that isn't what will be happening. But if he is just excited to be a new dad and wants to know what it tastes like so he can know what things are like for the baby, try not to let that bug you. It's not unusual for a woman to take a surreptitious sip of some of her own expressed breast milk to see what the big deal is, and if women get curious about their own, of course husbands might also.