Honestly, I did exactly this. I did all the photography and videography as a gift for a friend.

if you want to be petty, tell them that by law, the pictures belong to you and you give them no permission to reproduce, reuse or post them in any form. its illegal for them to do so.

Honestly, ydi. NEVER photograph a wedding without getting paid in full before the day. Best thing to do, when they book with you have them sign a contract. This protects both parties incase something happens. Also, typically you should be requiring a downpayment at the booking with the rest due in full by the rehearsal.

You need new friends!

Simple, don't give them any photos, not even online watermarked ones, until you get paid in full.

You should consider it a wedding gift. That's why people sometimes hire they're friends for that stuff. To save money

Did you sign a contract? No? Well let this be your lesson. Business is business, friends are friends. You can do them a mates rate but you always put the agreement in writing.

Don't deliver the pictures until they pay. If you already gave them the pictures then explain to them that you may be their friend but they still need to pay you considering you are doing a service for them.

You should find yourself some new friends because no matter what they should have been professional if you're their friend or not and paid.

If you were my friend OP I would pay you extra for being even willing to spend the wedding taking photos and be thankful.