Friar Lawrence is trying to tell Romeo that if he loves way to much he’s going to get sick of it eventually. Friar Lawrence doesn’t wan’t Romeo or Juliet to get hurt (!!!) or regret what their doing in the long run just because they gave too much of their love in the beginning and later on their sick of each other. its very good advice, i doubt Romeo takes his advice because they both end up getting hurt and Romeo probably things he’s nuts for thinking that you could love someone too much. they are not moderate people at all, everything they do and say to each other is way over the top.