I have seen a few productions of Romeo and Juliet that play up the homo-erotic tension that Mercutio has for Romeo. Is there any textual evidence to support this assumption?

Mercutio's homosexual feelings towards Romeo are evident by the insistent and descriptive way he tries to turn Romeo away from heterosexual desires. He warns of herpes and talks of how foolish desires are: "O’er ladies’ lips, who straight on kisses dream, Which oft the angry Mab with blisters plagues

Because their breaths with sweemeats tainted are. (I.iv.75-81)". In fact, Mercutio gets so wrapped up in his attempt that after the monologue Romeo tells him to stop.

Basically this speech is seen as a jealous attempt to keep Romeo to himself and away from heterosexual temptations, thoughts or desires. (I.e. Juliet)