is they seke??? Because Seme said this time is my turn!!! so the first time the uke how to...

I also didn't really understand... especially when chef-san said "I want to put it in" but farmerboy got blamed for hurting chef-san's back [which is usally the uke that gets his back hurt and seme gets blamed]... it is really unclear to me. Perhaps he just meant last time farmerboy was drunk and came onto him and this time is his turn to take initiative? I like seke though so i wouldn't complain

ya his back thing is confusing ,
i wish there is extra so we can understand everything (￣∇￣") me to i like seke :$

if its about the seme's back, im sure he said smth like "the pain is originally from when i fell out of the bed" and when they did it, "this position is a bit.." so, maybe they did it with some uncomfortable positions and hurt the seme's back ? but who knows lol this is just my thought.

Yui's back was injured when he fell out of bed, not during sex. We are told this explicitly. As for whether they are seke or not, who knows. Sex is only implied and not explicit. So, they could be, but I took the, "This time it's my turn.", to mean it was his turn to make the first move since Setsu made the first move when he was drunk. It is safer to make assumptions based on what you know for sure than to make too many assumptions that are based on other assumptions.