Everytime you "tweet" here, your posting a Note to a relay. A relay is like a bulletin board. So if you write to a relay but your friend doesn't read that relay of course they will never see it.

You can find the relays your on in the top right corner of Amethyst. Tap on the fraction you see there. It will look like this 10/10. Your numbers will be different.

Just send one or two relay addresses to him, and ask him to join so you can follow each other.

I hope that helps.