I think its English and 19th century. It concerns 2 friends (or perhaps they are cousins, and perhaps one is less well off than the other?), one of whom gets engaged to a man who insists on being the first man she has loved. This is not the case, there was a romance previously and the friend is drawn more and more into helping her friend keep the secret, which causes damage to her own reputation, and risks her own romantic happiness. I remember in particular a lot of funny business involving love letters and a miniature portrait. The truth comes out at the end, and husband and wife are estranged, but then I think are reconciled by the wife's father on his deathbed?
Any help much appreciated, I am going insane trying to remember this!
