In the interest of time
A variant of the movie TiMER (2009). I recommend watching it, if you haven't already.
Read the story now
On a more technical note overall: The vignettes were disjointed. I didn't feel connected to anyone. Each chapter was too short to really know any of the characters (let alone care about them). The protagonist, despite being in every snippet, still felt one-dimensional. After the introduction, I expected something...intimate. An expose. Cracking open someone's diary and sniffing the pages. Sneaking inside their head; exposing the squishy underbelly. Sharing favorite experiences. Instead, it was all very matter-of-fact and emotionally detached. I do, however, know several writers who've grown numb to certain topics because of how frequently they must be discussed at length. It's a potential angle. I just don't feel like it'd be the ideal route here.
Now, oddly enough, I can accept being born with a forearm death predictor. Not so much the aspect of finding and immediately recognizing your soulmate. (Maybe these folks just got lucky.) Or an abrupt change in the countdown if your love suffers from 'wrong place, wrong time' syndrome. The preternatural aspect of said clock should account for these circumstances. Otherwise, how could you trust it? Same concept goes for it suddenly starting over. What's the use?
In the movie I mentioned, the devices are implanted. Optionally. Being born with one offers a new twist. But its laws should be consistent. I look forward to future edits or expansions.