As the title says, these aliens has silently been sucking out the feelings of eros/lust. which will make humankind extinct in a few hundreds of years.
These aliens are unquestionably very advanced, in fact, they can wipe out human life within an hour if so they wanted with both biological and technological weapons. They can even modify memories through light. But the aliens abhor violence, so they decided instead that they will let us go extinct. Not by war but by taking away the drive force of committing sexual acts or lust that will inevitably lead to reproduction. If there's no reproduction, then no human beings will be born.
These aliens can manipulate feelings to a very fine degree. But they can't control the human mind.
We don't know that these aliens exist. And they are, however, willing to accelerate our extinction through natural or biological means, but nothing to invasive like viruses or alien bacteria.
Practically they can incite wrath among the top echelons of the government and start a world war which will inevitably lead humans to develop technologies that will probably defeat the aliens or it will turn into a nuclear war which will turn the world uninhabitable that it will need a few hundreds of years and a lot of resources to re-terraform. So this is the best option possible to them.
If these can be fought by us, then the aliens will be willing to be brought to the negotiating table