Last night, she said
The singer is recalling a conversation he had with his significant other the previous night.

"Oh, baby, I feel so down
His partner expresses that she feels sad or depressed about something.

Oh, it turns me off
Her negative emotions are brought to a point where she's not interested in physical intimacy.

When I feel left out"
She identifies that her sadness is happening when she's feeling excluded.

So I, I turned 'round
The singer takes some action in response to his partner's request.

Oh, baby, don't care no more
The singer tries to shake off his feelings of being hurt or worried about his partner's attitude.

I know this for sure
He is confident in his decision and is resolute about it.

I'm walking out that door
The singer has decided to leave the situation and walk out of the place.

Well, I've been in town for just about fifteen-oh minutes now
The singer is introducing the idea that he is a new person in town, unfamiliar with the place.

Oh, baby, I feel so down
The singer emphasizes his negative mood once again.

And I don't know why
He is puzzled as to the root cause of his melancholy.

I keep walking for miles
To ease his stress, the singer is taking a walk around the area he finds himself in.

And say, people, they don't understand
The singer suggests that others don't relate to or comprehend his current state of mind.

No, girlfriends, they can't understand
He extends this idea specifically to significant others, including his own past girlfriends, stating they don't understand either.

Your grandsons, they won't understand
Even future generations, represented here by grandsons, will not be able to get what he's going through.

On top of this, I ain't ever gonna understand
The singer is expressing his resignation to never truly understanding what is causing him pain.

Last night, she said
The singer returns to the recounting of his and his partner's conversation from the previous night.

"Oh, baby, don't feel so down
This time, his partner encourages him to be less negative and try to feel better.

Oh, it turns me off
She implies that his negative attitude is again affecting their relationship's intimacy.

When I feel left out"
Like before, she links her sadness with a feeling of being excluded.

So I, I turned round
Like earlier, the singer takes action and tries to address the problem in their relationship.

Oh, baby, gonna be alright
He reassures his partner that all will be well soon.

It was a great big lie
The singer confesses that his reassurances were insincere and false.

'Cause I left that night, yeah
He states that he left their place that night, abandoning the conversation and relationship.

Oh, people, they don't understand
He returns to his idea that no one but him can really comprehend his problems.

No, girlfriends, they don't understand
This is repeated again, emphasizing how even people who are or have been closest to him cannot understand.

In spaceships, they won't understand
He dramatically states that even beings from another world will not understand his state of mind.

And me, I ain't ever gonna understand
The singer reiterates his feeling of not being able to comprehend his own issues too.

Last night, she said
The final stanza begins by returning once more to the conversation from before.

"Oh, baby, I feel so down
This time, the singer is the one expressing his negative emotions.

See, it turns me off
He suggests his own mood is affecting their intimacy.

When I feel left out"
Identical to his partner's grievance from earlier, the singer feels excluded.

So I, I turned 'round
The singer again takes some action, responding to his partner's request to address the problem.

Oh, little girl, I don't care no more
He decides he doesn't care and will not be dealing with the situation anymore.

I know this for sure
He is once again resolute and confident in his decision.

I'm walking out that door
Like the earlier line, he decides to leave and ends the song.