Am I infringing on someone by using a picture of them in a group and writing of there history ?

Generally speaking, people have a so called "right of publicity" which enables them to control the use of their image, usually in commercial settings. Although, you do not provide great detail regarding the nature of the postings, I advise the following. If this person is threatening to sue, you should certainly consult with a local attorney about whether this right, given the nature of the posting, can be used against you. Secondly, with regard to the "history" that you posted, you should also consult with that attorney to determine if any of the statements made were defamatory and can be used against you. Depending on those assessments, you can proceed accordingly.

Good luck.

Disclaimer: This answer is for informational purposes only and does not constitute general or specific legal advice, nor create an attorney client relationship.