Word to describe someone who doesn't appreciate what another person has done for them

What is the single word to describe someone who doesn't appreciate what another person has done for them?

For example, let's say someone has sacrificed a lot of things and gone through a very hard life to make their spouse happy but the spouse leaves the person for very minor selfish reasons.

In other words, someone who is not appreciative of what the other person has done for them and never thinks twice to hurt the other person in exchange for the smallest benefit.

Solution 1:

If it has to be a single word (I assume you mean a noun), then ingrate fits the bill. It's still in common speech, but only just. It has a slightly antique flavour.

Solution 2:

You can use the adjective ungrateful.

Solution 3:

There's probably a few options here, but I'd suggest self-involved

self-in·volved (sĕlf′ĭn-vŏlvd′) adj. Absorbed primarily or only in one's own interests or activities.

Meaning

Solution 4:

If he/she regularly puts themselves first at the expense of others, is seemingly incapable of acknowledging the hardship of others, and it is a recurring feature of their personality rather than just an occasional oversight, they could be considered as narcissistic.