In the first couple of acts in Romeo and Juliet, Romeo's love is presented in two ways. First, his love is presented as being far too intense, overpowering, and irrational. Secondly, his love is presented as being that of a young school boy's love: his love is really more about physical attraction than anything deeper.
We see just how unhealthy, overpowering, and irrational Romeo's love is in the very first scene. In this scene, we learn from Romeo's father that Romeo has lately been staying out all night long, sleeping during the day, and has also been seen each morning at dawn standing under a certain grove of trees in a certain part of town, crying. Lord Montague sees that Romeo is in such a deeply troubled state of mind that he is afraid Romeo will do himself harm if Romeo continues not to confide in any one about his problem and continues to reject advice, as we see in Montague's lines to Benvolio, "Black and portentous must this humour prove / Unless good counsel may the cause remove" (I.i.137-38). Since Romeo's mood is "black and portentous," meaning in danger of wreaking havoc, like causing death, we know that Romeo's love is far too intense and far too irrational. He is allowing himself to be governed by his irrational emotions rather than his rational mind.
In addition to being far too overpowering and irrational, Romeo's love is also like a young school boy's. He has mistaken physical attraction for the deeper sentiment of real love. The only reason why he felt he was in love with Rosaline is because he thought she was beautiful. Likewise, the only reason why he has so fickly switched from loving Rosaline to loving Juliet is because he now thinks Juliet is far more beautiful than Rosaline. Romeo proves he has mistaken real love for mere physical attraction in his lines, "Did my heart love till now? Forswear it, sight! / For I ne'er saw true beauty till this night" (I.v.54-55).
Love can be categorized in three ways, Eros, Phiia, and Agape. Eros is categorized as love that is romantic, sensual, sexual, and full of desire. The love you hold for someone who is more than a friend. Philia is the love of friendship and loyalty towards family or community. Agape is the most complex love, also known as sacrificial or unconditional. Agape can be seen as both eros and philia and goes beyond mutual interaction. Therefore, his love at the start of the play is more of an Eros, or a lustful love that seems more sensual or full of desire towards Rosaline rather than anything else.