L.B.
He loves her, but he is extremely jealous of the time you are spending with her, which is why he is acting up so bad while you are feeding her. You should continue to feed her, and ignore him, unless he is doing something where he is going to get hurt. He knows if he throws a fit, you will stop with her and tend to him. Try your best to ignore any outbursts from him while you are feeding the baby. Any attention, negative or otherwise is what he is looking for. Finish feeding her, and then tend to him. Spend time one on one with him when she is napping. Maybe you could try getting him to help with feedings. Getting the bottle, rubbing the baby's forehead, or something. Maybe as simple as putting on his favorite video before you start feeding the baby.
Good luck. It's all about his not wanting to share you. He had your undivided attention for 3 years. Very common for young children with new siblings.