This HaBO comes from Veronica, who wants to find this book:

I think it was a Regency romance published in the late 80s or 90s (probably 90s). The heroine has a fight/misunderstanding with the hero and ends up going to Paris to stay with her aunt/grandmother for the season.

She meets a poor artist named Emil/Emile (?) and has an affair with him. He dies of consumption and she ends up meeting the hero again at society functions, who wins her over.

I feel like we don’t often see heroines getting involved with other characters. Curious to know if we can locate it!