In Romeo and Juliet, where are some key examples that prove the two are in love, or, on the other side, examples that prove they only feel lust?

The night that Romeo and Juliet first meet, he comes in secret to the garden beneath her balcony.  If the pair only felt lust for one another, it seems like they would have tried to do more than just talk.  Instead of engaging in some sort of conversation about sex, or Romeo attempting to climb up to Juliet's window, and so forth, Romeo only desires "Th' exchange of [Juliet's] love's faithful vow for [his]" (2.2.127).  Further, if he were only interested in Juliet sexually, it seems unlikely that he would be willing to marry her.  He lusted after Rosaline, but making her an offer of marriage never seems to have crossed his mind.

Moreover, if Romeo and Juliet felt only lust and not love, it doesn't seem likely that they would be willing to die for one another.  If Romeo were only interested in sex, I'm sure there are a number of women in Mantua that he could hook up with, but he loves Juliet, and so he is unwilling to live when he thinks that she is dead.  Further, if Juliet were only interested in sex, if she only felt lust for Romeo, then she wouldn't kill herself upon learning that Romeo has poisoned himself.  Lust doesn't cause people to feel that they cannot live without one another; only love can do that.