One of my favourite concepts in Buddhism is metta: this word is usually translated as loving-kindness, but its root meaning is the nature of a friend.
As frictions grow in life, we need to find more kindness and tolerance for everyone we meet. What's different in friendship is the chance to practice metta more deeply, and learn from our oversights. I recently noticed I was getting irritable with friends over minor mistakes. When I looked at this, I realised that I need to show more kindness to them - and to myself. It was my perfectionist expectations of myself and others that needed to be released, with kindness.
Metta is a very nourishing quality, and when we show it to others, we're also nourishing ourselves. This is a classic case of treating others as you would like to be treated yourself. Modern life expects us to be so up-together all the time: one blessing of friendships is that you should feel safe to show your failings, admit them, and still feel valued.
Another Buddhist teaching about friendship is the way a true friend is constant in good times or bad. It’s part of the wider Buddhist belief in a non-attachment to material circumstances. This is all a useful reminder of what resilience can mean for us.