Cheating in a romantic relationship is one of those things that many naively believe will never happen to them, but is common enough for a large proportion of people to experience at some point. There are a lot of dimensions to a serious partner being unfaithful, and that can be difficult. One of these is processing the obvious breach of trust, as well as considering whether there is a future in the relationship. 

Further than that, though, there is also the difficulty of understanding how the infidelity fits into your wider social circle. Cheating is the kind of thing that those it happens to struggle with not just because of what their partner done, but also how their friends have reacted to it. If you share a lot of social contacts this can be even more difficult, especially if they act in a way that doesn’t feel like it is in your best interests.