Enjoyable romance book!

I liked that the plot was a little different than traditional: Darius is basically hired to secretly impregnate (willing) Vivian, to ensure the heir to the title and estate of Vivian's very old husband. So the first 3rd of the book is Vivian and Darius meeting and then going secretly to his property to do the deed many many times for a month to get her pregnant. Of course he teaches her all about how to be a sensuous woman and how to have some guts, which she will need to be strong after her husband dies and she has a baby to care for.
The second 3rd is after the two have reluctantly parted ways, during Vivian's pregnancy. They pine for each other and contrive to accidentally meet multiple times. Darius starts to show up more and more often and sort of becomes a family friend. Also, Darius deals with ridding himself of the women who were using him for their entertainment.
The last 3rd is really where all the plotting of the "bad guy" happens. Vivian bears a healthy boy, everyone is pleased, husband dies and Darius arranges to have the bad guy blackmailer out of the picture so that he and Vivian can have their happily ever after with their child and they still get the money and estate, hurrah!

I liked that it wasn't a standard telling, and that though their feelings for each other could have developed a bit more slowly and genuinely, it wasn't insta-love.
I also liked that both Vivian and Darius were very "true" to each other--they didn't doubt the other person and really had their measure and trusted them. It was nice to see that the obstacles to them being together were society and the bad guy, not something that one did that was misunderstood.
One thing that I thought was not well done was the bad guy plotting. I thought it was a bit unclear what was going on (like what was Portia's role???) and it was very obviously pointed out that the carriage was seen early on, so that whole development was weak for me. Also poorly done were time changes, meaning that you'd be reading along just fine and then the paragraph immediate after the end of a dialogue would bluntly say 'Darius continued to pine for Vivian as he plotted for the next few weeks, until he happened to spot her one Thursday...' These transitions were crude and obnoxious, I would have preferred perhaps a formatting change instead, where the use of asterisks or a page break would have been clearer and somehow more elegant.