The Lovers is the card of love, of love triangles and choices. It's about acknowledging who/what will complete us and about making (or not) the choice to pursue the object of our desire. The Death is a card of fear and endings and it show experiences or events that will transform us either we want it or not. The combination of the Lovers and the Death shows a difficult relationship that's either ending or is being deeply transformed.
The elements of the cards are Air (Lovers) and Water (Death). We have Logic opposite Emotions. That's why the choice the Lovers represent will be a battle between what is right according to common sense and what feels right. Air/Water combinations are not really difficult per se, they're rather neutral and could go either way, positive or negative. However, the challenging aspect of the Death card gives this combination a less than benign tone. There's the promise that after the Death experience, we'll be wiser, stronger, a better version of ourselves, but that will come after we've shed the old skin, which is not always without a certain amount of discomfort.