One thing we can surmise from the very first scene is that Romeo's initial take on love is that it was purely a physical outlet. While he felt intensely passionate about Rosaline, it is obvious that he was not thinking in terms of commitment as he never mentioned the subject of marriage. We can surmise this from Romeo's statements about her beauty and her chastity, such as the lines:
She hath Dian's wit,
And, in strong proof of chastity well arm'd,
From Love's weak childish bow she lives unharm'd. (I.i.211-13)
Diana is the Roman goddess of both hunting and childbirth and, as the goddess of childbirth, is ironically known for her vow of chastity. Therefore, what Romeo is saying in these lines is that Rosaline has rejected him because she is also vowing to remain chaste. But if a vow of chastity was her answer, then what exactly was the question that Romeo posed to her? It most likely was not a marriage proposal; instead, he probably merely asked her for a romantic tryst. In other words, he merely wanted to seduce her rather than do the honorable thing, which was marry her. Romeo's actions are also a sign of his longing to seduce Rosaline, such as staying out all night long and being spotted each dawn crying under a grove of trees in a certain part of town. We can assume that the side of town is probably where Rosaline lives and the grove of trees probably offers a view of her house, most likely, even a view of her bedroom.
At first, after he meets Juliet, Romeo's actions still seem to portray his intentions of only a romantic tryst; it's Juliet who changes his attitude toward love, making him think more of commitment--honorable marriage. We can see that Romeo's actions immediately after meeting Juliet still lean more towards wanting a romantic tryst when he scales the Capulets' garden wall in hopes of seeing Juliet again. This action is no different from how he behaves towards Rosaline--hovering outside of her bedroom window in the hopes of satisfaction, or at least seeing her again. In addition, we can see that Romeo only has sexuality on his mind when, speaking to himself in his soliloquy, he metaphorically tells Juliet to take off her clothes, as we see in the line, "[The moon's] vestal livery is but sick and green, / And none but fools do wear it. Cast it off" (II.ii.8-9). In these lines, the word "vestal" can be translated as virginal, and livery refers to clothing or a uniform. Hence, he is saying here that the moon's virginal clothing is "sick and green" and tells Juliet to take off her virginal clothing. In addition, when Juliet later asks him, "What satisfaction canst thou have to-night," his only response is to ask for her vow of love (132-33). It's Juliet who, refusing to be dishonored and seduced, turns the conversation to marriage. It's Juliet who tells him that if he is thinking of marriage then to send word to her tomorrow. Therefore, it's Juliet's determination to remain honorable that influences Romeo's attitude towards love, making him also want marriage rather than just a romantic tryst.