1. Go to the Brothel in town( found in the Red Lantern District), request that your slaves can work there, and complete the side quest(any type of elf will work). Note, not every race can do sex work and not every slave will agree to do it(depends on traits or quest line status).
2. Prior to version 1.0, ropes cost 15 gold and were never returned, unless using certain mods. As of 1.0, ropes cost 50 gold and have a global durability(one value for all ropes owned by the player), which starts at 100% and subtracts 10% for each use(5% during sex). The decrease only effects the next use, so a rope is guaranteed to never break when fresh. In 1.0b, I fixed some cases where ropes could disappear without breaking.
My goal for this system was to avoid significantly changing the balance of the game and allow ropes to be used more than once. I tried to achieve this by ensuring that the average re-use case has a similar gold cost to the single use (ignoring the cost during sex, which is generally much lower than before). I also tried to avoid having a high cost worst case. The worst case(10% of total cases) is breakage after 2 uses, which has a cost of 25 gold per use. The average case(21% and 20% of total cases) should be breakage after 4 or 5 uses, which have costs of 12.5 or 10 gold per use. Getting more than 7 uses from the rope is rather unlikely(6% of total cases). The average cost of rope across all cases is 12.49 gold per use, but the players will generally feel that this is biased more towards the less favorable cases because they will tend to notice it more when they are unlucky.
edit: clarification of cases and added a bit more