As noted, to the extent that any drug will consistently evoke sexual desire under all conditions that's probably not a good thing (John McAfee and his cathinones, etc.). That said, mesembrine has anxiolytic effects and intensifies physical pleasure. It has long history of use as a sex drug, both traditionally in South Africa and with modern extracts, and people sometimes liken the experience to a low dose of MDMA. I don't think that's the most important benefit of the drug, which also causes longer-term mood elevation, but it's definitely there.
Mesembrine is currently legal in most jurisdictions, and standardized extracts are sold openly. Dried and powdered Sceletium tortuosum is also sold, but the material I've bought has all been very low quality. The plant is easily grown and yields well under hydroponic conditions similar to cannabis, lots of details in my comment history.