Hey aus_designer,
There is a very large expat community, with the majority being as friendly and welcoming as you would expect. I do know a gay couple who are based in Port Moresby (is that where you are looking?). They have been here about 2 years and quite enjoy it. I'm sure there is others (I'm relatively new myself so still meeting people) but I can't imagine your sexuality causing issues within the expat community. As you said, public areas will be different, but otherwise I think it shouldn't be an issue.