Date Night

I know this might sound ridiculous but I am a first time mom to this beautiful little boy. My husband got me tickets to see Ed Sheeran in July! Our baby will be 4 months old. My sister has agreed to watch the baby for the night but I am having soMe anxiety about it!
 I'm scared my baby is going to feel abandoned... I know moms leave babies all the time but I just can't get the thought out of head!
 Also I'm breastfeeding. If I pump and feed before we go... will my breast become engorged if I don't feed my baby for more than 4 or 5 hours?