You
Referring to the subject of the song

You'd fall in love with anyone
The subject has a tendency to fall in love easily

I'd think you'd fall in love with anyone
The singer believes the subject will fall in love with anyone who falls in love with them

Who fell in love with you
Describing who the subject will fall in love with

And they frequently do
People tend to fall in love with the subject

So take comfort
The subject can find comfort in their ability to easily attract love

Cruel comfort
This comfort is not necessarily a good thing, as it can lead to problems

Before you start to wonder
Advising the subject to think carefully before over-analyzing their situation

How you got locked inside your room
Describing a sense of feeling trapped or stuck in a situation

And how long will it... take?
Questioning how long it will be until the subject reaches a breaking point

Before you start to hate yourself
Implying that the subject will eventually begin to dislike themselves

And go straight to the arms of someone else
The subject may seek comfort in a new partner

And I'll just... wait
The singer will patiently wait for the subject to come back to them

'Till those arms belong to me
Describing the hopeful outcome of the situation

And I'm not saying that you love me
The singer is not making any particular assumptions about the subject's feelings towards them

I'm not saying any... thing
Further emphasizing that the singer is not making any definitive statements

Tell me
The singer is seeking information from the subject

Do you let them down, gently?
Asking if the subject is kind when breaking up with people

Does is only make it harder?
Wondering if being gentle actually makes it more difficult for the person being broken up with

To let the feeling linger
Describing the act of prolonging one's feelings

To drag it out a little longer
Further emphasizing the idea of prolonging feelings

Does it put your mind at ease?
Questioning the subject's own emotional state when going through a break up

But you're the one who brought 'em here
Reminding the subject that they chose to enter the relationship

You're the one who has to take them when you leave
Implying that the subject is responsible for the emotional consequences of ending the relationship