Not bad!
Not much to say story-wise this far since we only really have a fairly surface-level introduction to these characters, but what's there is good for setting up future antics.
Visuals were really well done for the most part. Arthur and Vivian generally look great, though Arthur looked a bit... plastic-y in the intro? I think that might have been an effect on him to make him look wet? I stopped noticing it later on for sure. Rabbits personally don't do anything for me so I'll reserve my thoughts on the third character. Some of the shots were also fun, like having the phone screen reflected in Arthur's eye.
Sex scene was well-blocked, I thought the animations were smooth and looked good. Also liked the ability to rotate through positions regardless of which one you picked first.
I did notice a few typos, punctuation errors, missing words, etc. but nothing that was overly distracting or inhibited my enjoyment or anything. Maybe something to just take one more proofreading pass before publishing.
I'm not sure what the future plans are for this, but it would be interesting to see the dialogue options have a bit more of an impact on the scene. I think pretty much all of them in this game with the exception of turning Vivian down are just flavor text for the immediately following lines, which is fine, and I think any player interaction is better than none, but it would be nice to see some callbacks or have previous interactions affect how the scene plays out in some, even subtle, way.
As a final comment, I think this is what Mausakrobat28 is trying to say with his, but naming this as "Version 1.0" might be a bit misleading. While there are no hard rules for versioning nomenclature or anything, usually "1.0" means the first full release. Since this is just the first chapter you should probably 1) clarify that this is still in progress somewhere in the description; and 2) change the version number to something like 0.1.
Looking forward to seeing more of this!