These are two separate novels - Something Borrowed comes first, and Something Blue is the sequel.
I picked up Borrowed because I saw a preview for the movie that will be coming out soon and thought it looked funny and cute. The book is much the same way - very funny, and cute.
The star of our book, Rachel is soon to be serving as Maid of Honor to her best friend, Darcy. The problem is Dex - Darcy's fiance, and Rachel's secret crush. After a drunken 30th birthday party, Rachel and Dex hook up, and Dex confesses he has feelings for Rachel too. The question is - what are they going to do about it? Normally it's difficult to feel bad for someone in Rachel's position, but we're helped along by the fact that Darcy is self-absorbed, obnoxious and a real "cuss" about 95% of the time, and that Rachel is a sweet, supportive, never-doing-anything-for-herself type of girl. We really want Rachel to get some for herself for a change!
Blue is the sequel and told from Darcy's point of view - we get a summary of the ending of Borrowed, with her spin on things, and the story goes on from there. In interest of not spoiling anything I won't go into too much detail, but I will say I hated Darcy for about the first half of the book, and then my opinion changed.
Both books are worth a read if you want something fun, funny and romantic-ish. There is some sexual content, but nothing horribly overt, and some swearing, but again, not gratuitous.