I've lived in Port Moresby for a year now and seem do fine on my own. I live downtown (across from the Crowne Plaza) by myself. I am a 50-year-old female who, until recently, has been here alone. Now my husband is here as well, after finishing up a job in Nigeria, although he spends most of his time out of the city (Moro). He had no intention of coming to work with me here until he came for a visit. He could not believe the freedom with which I move around, compared to his Nigerian assignment, nor the friendliness of my national friends here. He's now decided to stay for a year. (He's 62 and getting ready to retire.)
I have to say I love it here, but am probably not a 'typical' expat. I work with a nationally owned company, Trans Wonderland Limited (TWL), so I don't have a lot to do with the ex-pat crowd. If I get 'hungry' to hear some American accents, I typically get online and Skype with friends back home. I also hang occasionally, with some Aussies I know from my work here, down at the Yacht Club. I find them to be a fun bunch to hang around, and the food, conversation, and atmosphere there are all good.
I almost never worry about moving about the city alone here, but I am also not one of those to take undue chances (something I learned from all those years of working in Houston!) I, too, have read the reports about the dangerous life of Moresby, but am still looking for it after a year. It might be here, but it hasn't affected me.
Good luck with your assignment. I hope you enjoy it here as much as I do!