SH+Never+knowing+when+it+might+end+But,+always+happy+to+see+it+start

The line, "Never knowing when it might end but always happy to see it start" shows that friendship is unpredictable, but you should always be happy to have the friendship. It tells the reader that during a friendship you can't think about what might happen, but you have to be happy during the time of it and be grateful for what you have.

I think, too, that the poet wants us to realize that we should pay more attention to the start of friendships and appreciate those awkward moments when strangers get to know each other.