People who live with a condition will be able to maintain strong friendships and relations especially if they can handle their condition well. It is the symptoms of bipolar disorder that affects  a relation and can make it a tough time.

Individuals with bipolar disorder experience periods of intense emotion and behavior known as mood episodesTrusted Source. A person may be unable to recognize the potentially harmful or undesirable effects of these mood episodes, leading to moods and behaviors that are not typical for them.
Now a person with bipolar disorder have episodes of depression and manic constantly appearing in a sequence. The intensity of the symptoms vary and the episode lasts for a week and sometimes longer.

It is difficult to understand bipolar disorder what the condition is and how to deal with it, learn how it affects your friend and help them through it.

How to be there for someone with bipolar disorder

• Communication: Facing the problems and understanding them will be hard, but knowing when and how to handle the discussions is something very important. Communicating things will help your friend figure out problems and it can prevent things get worse.

• Recognizing symptoms: Those friends who are around you most of the times can help one detect the symptoms of an episode which can help them seek some treatment.

• Reacting calmly and rationally: When your friend is exhibiting extreme behaviors related to the episodes it is important that you be calm about it. A friend can help the other by trying to listen to what they have got to say. When they outpour themselves they are relieving themselves which can lead to positive outcomes.

Sources - https://www.medicalnewstoday.com/articles/bipolar-friend#helping-with-treatment