"I have a good relationship with my friend."
Why do you need to use 跟 in this instance instead of 和？Could you also say, 我和我的朋友有好关系 ？Or 我对我朋友有好关系 ？
I believe that they wanted to stress the usage of 'with'. In which case 跟 is the correct choice. If the sentence was 'my friends and I have a good relationship', then I would have used 和.