He hasn't been with anyone ever since Yoshino and he started dating...
Also, what he does is called "honeypot." Sleeping with someone so they let their guard down and you gain useful information. That's how they were able to get out of the last situation they were in, cause the girl he slept with blabbed. Are there different ways to find information? Absolutely. But that's the one he's used to and the one he knows work well. Now that they're officially a couple however, we can only hope that he'll stop resorting to that.
lol why are you saying a "young girl" like he's not young himself? And what use is thretening when you can forge relationships that allow you to gain whatever information you wish to gain whenever you feel like it? From the sound of it, you're saying you would prefer he harmed her rather than pleased her into confessing information. Because if he threatens, then he will most certainly need to follow through. You don't just tell someone "do this or else..." and then when they refuse, you just keep pressing them without inflicting physical harm.
And disrespect? How? Did she love him? Did she have feelings for him? Did she not intend to end their engagement in a matter of a few months? So he owes her loyalties because he has feelings for her? I'm failing to grasp your logic. Having feelings doesn't mean he should be her loyal dog when she's told him she wouldn't return his feelings. The disrespect can only come into play now that they're a couple.
Whenever kirishima sleeps with other girls I keep on being disappointed in him. Almost dropped it when I thought he would sleep with Yoshino’s cousin but thankfully he didnt. Author kept on making poor excuses for his behaviour like he had to sleep with Nao for Yoshino? Lol what a joke, there are countless ways to tackle the issue. Anyway, I’m losing brain cells reading this ( ̄∇ ̄")