Mercutio, apparently a haunted former soldier, could, perhaps be termed a "nihilist". His attitude towards love, therefore, is the same as his attitude towards just about everything else: it's all ultimately meaningless. Despite this, Mercutio has an immense appetite for life's simple pleasures (friendship, drink, wordplay, horseplay, swordplay), but he has killed for the state, has seen death, and he senses the futility of life and all its machinations (such as the ancient and pointless ongoing feud between two otherwise perfectly respectable families). Mercutio is given to us by Shakespeare as something of a foil for his friend, Romeo. Younger and still idealistic, Romeo does not live as recklessly as Mercutio, but, because of his aged cynicism, Mercutio would seem incapable of loving anybody with the same dedication as Romeo.
Find text to back this up yourself. Scan all of Mercutio's monologues and exchanges with Romeo. Look for the word "love" to begin with, but also take note of his fun-loving yet fatalistic approach to all things. Personally, I would begin with the "Queen Mab" monologue, beginning in Act 1, scene 4, line 53...
Mercutio is quite practical about love and sees it more as an annoyance and a burden than anything else. His comments about the topic during his conversation with Romeo in Act 1, Scene 4 makes his sentiment very clear. He advises the lovesick and troubled young Montague:
If love be rough with you, be rough with love;
Prick love for pricking, and you beat love down.
In this extract, he ambiguously refers to both the emotion itself as well as the one who provokes it. He tells Romeo that if he is treated roughly by love or the one he loves he should return the sentiment and be equally abrasive. Furthermore, if he is hurt by love or by his beloved, he should, likewise, return the favor. He is, in effect, telling Romeo that he should not become a victim but that he should "beat love down." In other words, Romeo should fight back and withstand whatever injury he may encounter from love itself or the object of his passion.
In Act 2, Scene 1, Mercutio confirms his cynicism about love. When Benvolio tells him that Romeo's love is blind, he replies:
If love be blind, love cannot hit the mark.
He suggests that blind love cannot target anyone since it cannot see its mark and, therefore, cannot hit it. In essence, (romantic) love, according to this interpretation, is meaningless.
In addition, Mercutio's sentiments about love prior to the above statement clearly indicate that he sees it as a purely physical pursuit. When he speaks about Romeo being lovelorn, he repeatedly alludes to the sexual act and the desire which so-called love inspires. He mentions that he can encourage Romeo to come out of hiding by merely mentioning Rosaline's physical and sexual attributes:
I conjure thee by Rosaline's bright eyes,
By her high forehead and her scarlet lip,
By her fine foot, straight leg and quivering thigh
And the demesnes that there adjacent lie,
Mercutio's cynicism is further accentuated by his remarks regarding Romeo's feelings for Rosaline. He mentions in Act 2, scene 3:
Alas poor Romeo! he is already dead; stabbed with a
white wench's black eye; shot through the ear with a
love-song; the very pin of his heart cleft with the
blind bow-boy's butt-shaft
He is clearly harsh about the dire consequences of infatuation and unknowingly foreshadows Romeo's tragic destiny in what he says.
Mercutio's lack of belief and his practical approach are offset by his mercurial and impulsive nature. He is quick to anger and it is this aspect of his character that brings about his untimely demise.