Oh, the 'Even if I Regret It Now' hunt! I completely get why you're looking—those manhwa titles translated from Korean sometimes end up scattered all over the place.
For this one, the official and highest-quality place to read it is on Tapas. That's where the official English translation is being serialized. The art is crisp, the translation flows well, and you're supporting the creators directly, which is always a plus. It updates regularly there, too. I'd really recommend starting on Tapas to get the best experience.
Now, I have to warn you, I stumbled onto some aggregator sites while searching, and the quality was all over the place. Some had terrible, machine-translated text that made the story confusing, and others had watermarks splashed everywhere. It really ruins the mood for a story that relies so much on emotional nuance. So while you can technically find it on those free sites, the drop in quality isn't worth the convenience.
Honestly, the main character's journey from regret to whatever comes next is handled with such delicate art that you'd miss half the impact with a sloppy scanlation. Just my two cents—I'd bookmark the Tapas page and maybe use their free ink system to check it out.