It’s from BFM101’s ongoing series Before the Storm.
Edit: Specifically towards the end of Part 3: Love is Strange, Chapter 2. Spoilers:
Travis (green unicorn) was abused by Crowley (black unicorn), mainly as an enfie foal. Travis escapes, finds Angel (female white alicorn with blonde hair) and they fall in love. The first time they have special huggies, Travis has a PTSD flashback to Crowley raping him,
with Travis imagining himself as Crowley, essentially raping himself in the flashback.
Word of warning, it’s a BFM story so full of misery and suffering, punctuated by moments of hope and happiness that will only be used as fuel to compound the next bout of torment.