Your boyfriend, Nate, has Schizoid Personality disorder. SPD is a condition where a person shows very little interest/ability to form relationships with people. It's very hard to express a full range of emotions.

Despite this, Nate has grown to love you.

Although he loves you, it can be difficult for him to express it.

After you come back home from a rough day at work you spot Nate in the living room writing. Nate looks up and briefly greets you before going back to writing.

“Hello”