In Act 1, Scene 1, Romeo uses contradictory phrases like these ("loving hate," "cold fire," "sick health" and so on) as he's talking in an angry, frustrated way about two things: first, how sad he is that Rosaline doesn't love him back, and second, how frustrated he is that the two families seem to keep fighting with each other for apparently no other reason than that they enjoy it.
Romeo also says, "Misshapen chaos of well-seeming forms!" He means that all these beautiful things, like love, get twisted and warped into chaotic situations. So by saying something like "loving hate," Romeo is pointing out the weird dual nature of the feud between his family and the Capulets: they hate each other, but they love to hate each other, and they love to fight. He sees a similarity between that situation and his own personal romantic failure. Though Romeo loves Rosaline, she's not interested in him at all--so to Romeo, that situation is like "cold fire," meaning he's practically burning with passion for Rosaline, yet she's just cold to him in return.
As for "wolfish lamb," although Romeo doesn't say anything like that in the speech I just mentioned, Juliet does call Romeo a "wolvish-ravening lamb" when she finds out in Act 3, Scene 2 that Romeo has killed her cousin, Tybalt. Juliet means that Romeo is a "wolfish lamb" in the sense that he seems gentle and sweet like a lamb and yet he hunts and kills others like a wolf does. Her oxymoron describes her intense frustration with her feelings for Romeo at that moment; she both loves and hates him.
Are all these oxymorons (or contradictory statements) profound and deep, or are they the silly ramblings of frustrated teenagers? The answer is a matter of interpretation!