We learn several things in the second act about Friar Laurence's perspective on love. In particular, we learn that Friar Laurence views youth as fickle and youth's love as insincere. We also learn that he thinks the heated, passionate love that Romeo and Juliet share is not genuine love and likely to die soon. Finally, we also learn that he believes that love can put an end to hate.
We see Friar Laurence express his view that youths are fickle as a result of insincere love when we see him reprimand Romeo for changing so suddenly from loving Rosaline to loving Juliet, as we see in the lines, "Young men's love then lies / Not truly in their hearts, but in their eyes" (II.iii.68-69). In other words, Friar Laurence is accusing Romeo and all young men of equating love with physical attraction, which is not the strongest, most sincere form of love. When Romeo defends himself, declaring, "Thou chid'st me oft for loving Rosaline," we further see Friar Laurence accuse Romeo of insincere love when he says, "For doting, not for loving, pupil mine" (82-83). The term "doting" can be translated as "being infatuated with." Infatuation is an intense, foolhardy passion that is also very "short-lived" (The American Heritage Dictionary). Hence, in accusing Romeo of being infatuated with Rosaline, he is declaring his perspective that youths do not truly know what real love is and instead mistake love for foolish passion, which does not last long. Thus, Friar Laurence is declaring his perspective that youthful love is fickle and insincere.
We also see Friar Laurence refer to a second perspective on love that closely relates to his view concerning the fickleness and insincerity of youthful love. Not only does he think that Romeo's love for Rosaline was insincere, he also thinks that the love Romeo and Juliet share is equally insincere and likely to die soon. We see Friar Laurence express this perspective when, before conducting their marriage ceremony, he warns them that violent, heated passion is likely to end suddenly and violently, as we see in the lines:
These violent delights have violent ends
And in their triumph die, like fire and powder,
Which, as they kiss, consume. (II.vi.9-11)
Hence, Friar Laurence is also expressing his perspective that love based purely on violent passion is insincere and likely to end suddenly.
Finally, Friar Laurence also relays his perspective that love can conquer hatred and that hatred is sinful and, therefore, everything must be done to put an end to hatred. We see Friar Laurence relay this perspective when he agrees to marry Romeo and Juliet that day even though he thinks it is unwise and that their love for each other is youthful and insincere, as we see in his lines:
In one respect I'll thy assistant be;
For this alliance may so happy prove
To turn your household's rancour to pure love. (II.iii.93-95)
In this passage "rancour" can be interpreted to refer to "bitterness," or hatred thereby showing us that the only reason why Friar Laurence has agreed to marry the couple is that he thinks it will put an end to the sinful family feud, which shows us his perspective that love can conquer hatred.