Thanos' motivations in the film will follow closely what we saw in the comics, according to Kevin Feige, who said "they’ll be similar to what they were in the Infinity Gauntlet in various ways."
The suggestion there is that Death will appear as the object of Thanos' affection and the reason he seeks to change the universe.
That's as vague as vague can be, as you'd probably expect from Feige, but the fact that he reveal the similarity is pretty telling.
Could it be that the film will actually follow the narrative of the comics recently and have Hela replace Death as Thanos' love? Given that Cate Blanchett's villain exists in this universe, it wouldn't be too much of a stretch, and the more we see of her the better, quite frankly.