“Are bipolar people manipulative?”

Not any more so than people without mood disorders. If a person with bipolar disorder also has a personality disorder, like Borderline Personality Disorder, you may see more manipulative behavior from that person.

Being manipulative is not a characteristic of Bipolar disorder. You are describing something that is a problematic behavior not necessarily associated with a specific diagnosis. Be clear with the person about what you will and won't do - in other words keep your boundaries. This is the best way to handle manipulation.

Nancy J. Warren, PhD

They are, or they can be, because they believe they have skills to do great things or they do not. They alternate between these two extreme beliefs. Either/or. I emphasize beliefs over knowledge. They have such low self-esteem within that they have to convince themselves and the world outside that they are special. They were raised to believe they are special, because they come from a special family or a family of special expectations. However, they were not nurtured into the skills of success. They don't understand how achievement is created by perseverance and hard work. They have some magical thinking: If I believe it, it is so. They act "as if", and ultimately it backfires, so they hit bottom in despair over the alternate belief that they are worthless and will never matter. When the pain is too great, they dissociate and have a sort of "religious experience," and re-discover how magnificent they are. Then, they "act as" if to prove it.

Being bipolar doesn't make them more or less capable of being manipulative. Just being human causes that. Having said that, some people will use their diagnosis as an excuse for bad behavior. Don't accept that. Being bipolar doesn't give them an excuse to be abusive or manipulative. Hold him accountable for his actions. He could be seeing you excuse his behavior or acting guilty and using it.
If this is new behavior it could be linked to his medicine. Please tell the Dr about your concerns

People who have a diagnosis of bipolar disorder are not manipulative by nature. Symptoms of bipolar disorder involve manic (bipolar I) or hypomanic states (bipolar II), symptoms of which can lead to increased impulsivity and other risk-taking behaviors, which may involve actual manipulative behaviors, or manipulation as perceived by others.

Take a peek at this link regarding your question:
https://www.bipolar-lives.com/bipolar-and-lying.html