i think it's the case here T_T He's an idiot!!!!! Why can't he, for once, fall in loveand enjoy?! :'(
Yashiro is already in love with Doumeki, I think the reason why he kept sleeping with others was because Doumeki previously didn't show any interest plus he was impotent so Yashiro thought he didn't have a chance with him. Since Doumeki sucking him off was an order at first, hence again Yashiro thought Doumeki was simply following the orders of his boss.
But yeah, him wanting to sleep with Doumeki now is because he's planning to push him away. But I think it has more to do with him trying to protect Doumeki from what's to come next. The phone call from before proves it.
As usual I'm blown (heh) away, I love that even amongst all the Yakuza craziness Sensei brings it back to Yashiro and Doumeki! I just hope Yashiro suggesting sex so bluntly isn't some convoluted idea to push Doumeki away.