EchoBitch - I really don't think it's that black and white. There are shades of grey in this. Basically if your partner considers it cheating then it is. If they wouldn't in fact be too concerned about it, then it isn't - well not in that absolute sense of the word.
I think that most people would agree that having an affair and sex, with someone else of the same sex as your partner, without your partner knowing, is cheating in the accepted sense of the word and most partners would be upset about it.
However there are many shades of grey (no reference to the dreadful book intended). For example if it's a purely emotional affair - no physical contact whatsoever. People's reaction to that can vary enormously. Some would consider it to be unforgiveable cheating. Others wouldn't.
What about if it's only occasional visits to a prostitute we're talking about. And that is to satisfy some desire that the partner is unable/unwilling to satisfy. If a partner were to find out about it they may well find it quite distasteful, but might understand the reasons and find themselves able to forgive it, and also not categorise it as cheating per se. Others would consider it cheating.
And if my male partner were to get drunk and end up having some sort of sexual contact with another man, perhaps because he'd always wondered what it was like, but he knew he was basically straight, and I found out about it, then I wouldn't consider it to be cheating. I might be upset that he hadn't told me about it because I would like to think I'm the sort of person he would feel able to tell that sort of thing to, but apart from that I really wouldn't mind. I would't feel jealous, as I wouldn't be worried if he is younger/prettier than me or whatever. I wouldn't have to ask 'what has he got that I haven't?' as I already know the answer, and I would understand that my partner would have no romantic interest in men, so our relationship wouldn't feel threatened. So for me it wouldn't be cheating.To some other people it would be.
And there are lots of men who would not be the least bit bothered about their wife or girlfriend having a one-off sexual contact with another woman, and there are some who would.
So you really can't say all these things are cheating. Only the individual partner in each particular situation can make that judgement in each particular case, depending on how they feel about it (or would feel about it if they find out). And the 'cheater' can also make an educated guess about how their partner would react, as presumably they know them very well. So if the OP doesn't sound guilt ridden enough for the liking of some of you, maybe it's because she is fairly sure that her husband/partner wouldn't react that badly.
Sorry for the long post.