I also recommend: 'One Warm Word' (there are 2 couples that are the main leads - so it's 4 characters - one couple the man is the one cheating, whilst the other couple it's the girl who is cheating on her husband).
and 'My Wife is Having an Affair this Week' - the woman is the one cheating.
I only watch dramas that show the painful and redemptive side to affairs when I watch "affair" dramas.