So, your teacher is your virtuous friend He could, also, be called your guru.
The difference between your virtuous friend and your normal friend is that the guru represents other aspects. The guru is the living embodiment of what you want to achieve.
Sometimes it is difficult to think of your friends like that because we are all striving. We are all in the same boat. At least the guru is a living example.
To express it simply, for me, a Buddha would be the perfect, the most advanced version of a human. The best version of a human being would be a Buddha. At least, this is from my perspective. This is an easier, down to earth, kind of conventional way to see it.
So your guru, you visualize as a Buddha. You see him as the best version of a human. That is what you are striving to reach. You are trying to attain those characteristics. He is a shining example. The guru represents the ideal. The guru is helping you to see these features in you. Gurus are helping you achieve that potential within you. They are assisting you to actualize that beauty.
It is like we are coal. In coal, a potential diamond is inside there. We have to find it but the diamond is already there. We just have to recognize it.
Also, we receive blessings and inspiration from the guru. We rely on the guru for advice and teachings. His life is a living example that teaches and guides us. He is like the light that helps us see so we can walk our path quicker and easier, to understand the true nature of the mind and who we are being on the path.
You can, also, say that for a friend, but there is a different kind of perspective. It is a little bit different but similar.
I hope this is helpful.
Thangka by Christine Schnoell