Quoting Richard and samantha:" she told me something about the few weeks that the baby has to be breast fed or else if it has a baby it wont eat anymore other than the bottle she said it gets confused"
Baby shouldn't have a bottle for at least 6 weeks, but seriously it's not your job to feed the baby and there are plenty of other ways for dad to bond with baby other than feeding. Baby needs mom to breastfeed them, and mom and baby need you to support her. Do a little research on breastfeeding and you will discover that it's not just nutritional benefits it's also emotional ones. Daddy feeding them from a bottle doesn't give them those important emotional benefits.
You can help best by changing the baby, helping put them to sleep, and playing with them while your fiance gets a shower or eats something.