The market for romance novels is extremely saturated and has become swamped with popularity for aspiring writers to write the next 50 Shades of Grey.
A lot of these books follow a similar theme, but they're all tailored to becoming the next 50 Shades of Grey. As an author, I'd shift my approach to a less saturated market and try and find something that's still a romance novel, but also dips its toes into another category. Imagine a romance novel with a thriller style vibe to it... A completely different edge and setting but still that romantic approach.
Stand out from the norm is the vital thing to avoid failure, and keep marketing! Share online, go to every Facebook group possible, keep posting on Twitter, asking family and friends to do the same. A lot of books stay quiet because nobody is shouting about them, so as an author make it your mission to have your book heard.
I hope this helps but if you'd like to discuss the above in more detail or anything like that, feel free to get in touch with me :-)