Are you sure you want to spend 3 weeks, only in Sihanoukville ? I spent 6 days there & was ready to move onto Pattaya once that was done.
For that length of trip, you can visit 3~4 places, without feeling like you are constantly traveling. e.g. Bangkok, Siem Reap, Pattaya

I imagine the tuk tuk mafia can quickly procure whatever you need & if they don't, some of the scruffy tourist backpackers can probably advise you where to go. I've not tried anything, but have had offers.

Dating apps, well none were great when I was there a few years ago. You could test them by downloading a fake GPS app onto your phone & setting your location to there.