She was the last of the great pharaohs of Egypt and she must have been more than just a pretty face in order to attract the attentions of two of aoh of historys most powerful men.
It has to be understood that Cleopatra, as Pharaoh of Egypt, would have been used to the concept of polygamy. Marrying Caeser and Antonius while they were still married to their Roman wives was not unuasual to her and she may not have understood the Romans abhorance of it.
Also we cannot judge her by the standards of today where suicide is considered the easy way out as there are always solutions, people to talk to etc...... Back then suicide was considered an honourable way to end ones life.
Also while the surviving children were raised by Octavian's sister, only Selene was allowed to lived, Octavian killed Helios and Philadelphus.
My personal opinion, although I emphasise that it's just an opinion is that Octavian secretyly was in love with Cleopatra but she didn't return it, she spurned him and thats why he hated her while continuing to hide a passion for her. I find it strange that a man who supposedly hated her gave in to her request to bury Antonius's body, allowed the statue of Cleopatra Venus to remain standing and allowed Selene to live even creating her Queen of MAuretania in her own right as a wedding present to Juba King of Numidia.
Killing the males was something he had to do to avoid any further claims on the Egyptian throne although a female on egypt's throne would not have been unusual obviously. I think he had a soft spot for Selene but she may have reminded him of her mother. All just speculation obviously!