Great cover. The writing inside is very good imho. I think you will eventually draw more and more word-of-mouth sales, which are invaluable, as more readers discover and enjoy your book. (How's the marketing going? Have you found where you target audience is and figured out how to get visibility for your book there?)
Regarding the blurb, my suggestion is to consider condensing the first two sentences. I'm not sure how, but maybe the blurb needs to do something more to suggest what the reader might find in your story and to entice the reader to buy the book. Is it just abuse, uncertainty, and a relationship? There's much more, right? Like I said, I'm not quite sure how best to convey this, I just feel like there may be an opportunity here.
My feeling is that many people will enjoy the writing and story, and eventually sales will grow. I all hope your hard work pays off.
I dont really know enoug to write a whole blurb but how about starting with something like
"David likes being a wallflower, so a heroic rescue of the smart, funny and gorgeous Lucy, from a freezing Montana lake, was not part of his plan for that morning. Little does he know that one little rescue, will have far reaching consequences for his life."
I might also say something about him learning to come out of his shell, overcome his shyness/wallflower tenancies.
All seventeen-year-old David really wants is to fly under life's radar. In a typical cold winter day in Montana he does something extraordinary: rescues smart, funny, gorgeous good-girl Lucy Peterson from drowning in a freezing lake. As their friendship grows, David realizes that risking his life was the easy part. His friendship with a girl who is different from him in every imaginable way forces David to challenge himself and those around him. He must face the abuse of his past and the uncertainty of his future as he struggles to keep Lucy by his side.
Hum, I think I would leave the abuse thing out of it. If your main idea is a love story, then mentioning abuse might turn readers away. Let them find out later. Or, you could say something like -- "Brought up in the school of hard knocks, seventeen-year-old David (LAST NAME) really wants to stay under life's radar". --- This sentence is good. Change the first word to On, instead of In --n a typical cold winter day in Montana(,) he does something extraordinary: (he) rescues smart, funny, gorgeous good-girl Lucy Peterson from drowning in a freezing lake.
Now it is a little flat.
I suggest you take a good look at your first chapter, which I assume gets your readers hooked. Build your blurb from that and don't try to tell the rest of the story. Add a hook sentence to the end and you've got it. A hook sentence is something like...David could never have guessed what would happen next.
You're correct that the blurb is one of the toughest things to write. That's because you have about twenty seconds to grab the interest of a reader unfamiliar with your work. There is such a large body of work out there that you must hit them between the eyes with the potential of the book before they can leave. Your cover got them to the page, now your blurb has to make them want to read the sample.
I might have written something like:
On a freezing day in Montana, David does something totally out of character— he rescues smart and funny Lucy Peterson from drowning in an ice-covered lake. As someone whose goal in life might have been defined as remaining under the radar of fellow townspeople, the attention directed at him from local citizens and especially a gorgeous and grateful young woman, is— intimidating. As David's relationship with Lucy grows, he realizes that risking his life in that lake was the easy part.
Of course, everyone will have different ideas about what to include in the blurb and how to state it. This is just my opinion. Good luck.