Romeo refers to love early on because he thinks he is in love with Rosaline. He offers these words that portray love with allusion through images of smoke and fire:
Love is a smoke raised with the fume of sighs;
Being purged, a fire sparkling in lovers' eyes;
Being vex'd a sea nourish'd with lovers' tears:
What is it else? a madness most discreet,
A choking gall and a preserving sweet.
What makes this definition of love equal to hell is the fact that love does nothing but kill, which can lead to hell. It also shows love as a paradox, once attained, it drives someone almost insane. This is from Act I, scene ii.
Later, in scene iv, Romeo and Mercutio are talking about going to the Capulet's feast. Romeo doesn't want to go because Love is weighing him down. Here is their conversation:
You are a lover; borrow Cupid's wings,
And soar with them above a common bound.
I am too sore enpierced with his shaft
To soar with his light feathers, and so bound,
I cannot bound a pitch above dull woe:
Under love's heavy burden do I sink.
And, to sink in it, should you burden love;
Too great oppression for a tender thing.
Is love a tender thing? it is too rough,
Too rude, too boisterous, and it pricks like thorn.
If love be rough with you, be rough with love;
Prick love for pricking, and you beat love down.
Romeo paints the picture of love that it is excruciatingly painful. This is the problem of Hell. There is to be extreme pain. Romeo is living a hell on earth for having to exist without Rosaline's love.
I hope that is helpful. Maybe another editor can think of another specific place which refers to Hell more directly. I have had to work figurative examples for you.