The Wallflower, the Rake, and the Masquerade by Alanna Lucas

After years of being treated as a little more than a servant, Portia Lamont overhears her half-siblings plotting to send her to Town and marry her off. Since she has a paltry dowry and little else to offer a prospective husband, she wonders if she’ll even find a half-decent match, someone who’ll share her love of intellectual pursuits.
Titus Beaumont, Lord Ravensworth, is an unwilling participant in this year’s Season. All his adult life, he’s managed to avoid marriage, becoming a seasoned rake because he dares not risk his heart again. However, at his aunt’s insistence, he must attend for his cousin’s entrance into Society.
In the ton’s hectic marriage mart, Portia is considered a wallflower, an experience made even more vexing when she catches sight of Titus, her beloved childhood companion—the boy who once told her, I will always be your friend, no matter what happens. But when she was sent away after her father’s death, she never heard from him again. And time, a ruthless master, has not improved her circumstances. It seems he still wants nothing to do with her.
Except at a masquerade, when he doesn’t recognize her behind her mask and kisses her…
Sometimes the best revenge is just being yourself.