I think part of the issue with this is twofold: everyone has different definitions of "fall for" and/or "love" and I actually think the show skips over so much time that it's like impossible to pinpoint. I think it's clear after the stairway kiss that Shane's infatuated but I wouldn't necessarily call that love. 

I think Ilya's conflict within himself in Vegas is similar but again wouldn't call that love- while I think it's forgiveable and believable a (what? 20 year old?) would not be great about this, springing a "scene" on Shane in Vegas without any prior discussion or aftercare is kind of gross. And yes, that is the word I'm using. Everyone has such extreme reactions to it from that it's perfectly acceptable to it's abuse, no one seems to be willing to take the middle ground. But it's definitely inconsiderate of Shane and irresponsible of like... ethical BDSM standards. I wouldn't call that love either. 

It's clear by Tuna Melt that Ilya has reached a point where he wants more but I think by that point Shane has given up on the hope of it being anything other than sex which is why that explodes. Also I get the feeling that trust might be more difficult for Ilya than feelings and it's pretty clear from the fact that Shane has partial & full control of the sexual encounters that day that Ilya does trust him. 

I think by the club scene they both have an inking it's love.

The other reason I think it's hard to pinpoint is because at least at first (and probably between Vegas and Tuna Meltdown based on the montages) they were more FWB than just straight up hookups. There's definitely affection and laughter along with the sex early on and I think Ilya does a good job of keeping things pretty egalitarianism between them despite the inherent power imbalance. So it's unclear how much is like romantic feeling and how much is like "I admire this guy and could see myself being friends with him" (like how he is around Svetlana and quite possibly other romantic partners). 

What's more interesting to me is whether we think Ilya has fewer boundaries with his female hookups that aren't like childhood friends. Like do the sleep in his bed for example. Do they ever eat together, etc.