Is anyway possible for somebody to sue me for using first names of real people in my book about all of the things that I experienced in my life?

If the people are identifiable--that is, from the facts, the first names, the descriptions, etc., someone could tell who they are--then if anything you say is defamatory, they could potentially sue you. Defamation is making an untrue factual assertion about others. Note that even if what you say is true, if the person disputes it, they may try to sue you, which would put you in the position of having to defend yourself. For example: say you claim to have had sex with a married person while he/she was married. If it is possible to identify who that person was, he or she may feel compelled to sue you--even if what you said was true--to protect his/her reputation. And if you cannot substantiate what you claimed, you could lose the lawsuit.