Bail Out by Suzanne Winslow

Once he made up his mind, there was no changing it back …

At sixteen, Rachel Miller fell in love with her brother’s best friend. Eleven years her senior, Nate Doyle never gave her a second look. Nine years later, nothing’s changed—the handsome firefighter still keeps her at an arm’s length.
Raised in a traditional Irish family, Nate respects commitment. So much so that he has no intention of going down that road again. His relationships are measured in weeks or months, which makes his best friend’s sister off limits.
After watching Rachel get her heart broken again, Nate is no longer willing to stand on the sidelines. It means he must become a different man, if only Rachel can see the changes he’s made. This time, it’s too important to bail out.