Separation anxiety - 6 months old

Me and my husband went out for the evening after putting baby to bed and baby was being watched by their grandmother for roughly 5 hours. Grandmother said baby woke pretty much after we left and was inconsolably crying for nearly two hours straight.

Baby may see grandmother every week, if not every other week since they were born.

I know it’s normal for baby to have separation anxiety and am I right in saying it’s a good sign to have this attachment? But crying themselves to sleep is this not damaging?

I really don’t want to leave baby again knowing how distressed they got, but we have a wedding coming up in a couple of months that requires pretty much the whole day and evening apart. How do I help by baby so this doesn’t happen again?