Sometimes, the potion can be learned by studying back at home.. but:
Aphrodisiac: Water lilly + Blue Essence + Succubus leaf + [empty] + Green Essence
capturing Roushk only happened when Othra asks you to get him.. whither you are going bad or good route for the lizards.. however, i havent tried the bad route lately.
"get" as term of them loving the MC and increasing a heart, no. for the time being you may use the love potion on the Bartender, Shopkeeper, blacksmith or Filiar to have a scene [if you know what i mean]