With respect to men having long term girlfriends without marriage. Yes, I find it puzzling too, but most of these men are simply following society and women on their terms. And marriage confers very few rights on men in western society. On the contrary, once a man is married his "girlfriend" has much more power over him and is likely to be less anxious to please him.
In modern society it is considered "normal" for young women to not maintain a reputation of virginity before marriage, (even so-called Catholic, even "trad" women become extremely indignant at the idea that they should be expected to maintain such a reputation and that it be a true reputation) and because it is considered socially important for women to have long term boyfriends, (and for men too, to be accepted in worldly upper middle class "society") - many men have long term girlfriends. Also, the women typically use birth control, so this is another factor that enables them to have several long term boyfriends in succession as though it were normal without bringing children into the picture.
I think it's a relatively small section of men who will despise their conquests and move on to the next heartlessly. However, that small section of men tend to be the ones most successful with women. Being like a king's son - and having so many women willing to throw themselves at them, must breed in them a feeling of contempt for women.