We often identify love with friendship. Why is that?
Because they share common ground! In both cases, a break-up can be heart-wrenching when very strong emotions are involved. And the reasons for a break-up are often the same, too.
How do you mean?
Take the case of the woman whose husband secretly met up with someone else and the girl who felt betrayed because her friend didn't want to go on holiday with her: the feeling of betrayal in both situations arises from the same notion of exclusivity. Maybe the husband was being secretive simply because he was afraid of what his wife would say and that she wouldn't understand. And maybe in the second case, the other girl felt stifled by the friendship. That doesn't mean that she wants to end the relationship. It's important not to confuse wanting space, which is necessary in any relationship, with wanting to break up.
Finally, how do you get over a betrayal?
You need to analyze the situation and try to take a step back to find out why it's happened and how responsible you are for it. If the other person expains why, that can help too. Most importantly, you have to learn to live with the disappointment and be aware that it's not always possible to 'get over' an act of betrayal.