calendar

Your description isn't clear about what it is you are sharing with your friend. Did you accept an invitation for a single event or did you accept an invitation to share an entire calendar?

If the former, then the answer to your question is no, only the single event is shared between the two of you.

If the latter, yes; every event in that calendar will be shared. Read Accept a shared calendar invitation on iCloud.com

Any other calendar in the Calendar software is private to your device - or devices if you sync via your iCloud account. These are yours alone. Do not be limited to the couple of calendar names which Apple provides such as Home or Work; create others as you need them for specific activities.

You can "unsubscribe" from the calendar - at which point it ought to disappear from your Calendar software. Read Apple's instructions on unsubscribing at the foot of this page.