I think you are taking this way to seriously. It's just manga to read for fun not a RL couple.
that's a very one track view of them. they aren't teenagers, they are grown men and they both love and care for each other, thats obvious. aki is younger so obvious hes gona feel insecure but asami is smart and he knows what he wants, and he will always be there for the one he loves.
its not only sex they share. they live toghter. aki cooks for asami, they watch tv togheter. thats all shown in the extras. so in my opinion they do share a normal couple life. even in real life there are couples that only see each other at night. that doesnt mean that there is just sex. and its not like aki is a lonely houswife waiting for the husband to come home. he has his job too and is not allways at home when asami returns and they re both content with that. thats a great relationship if you ask me. and as stated by another reply above beeing a couple doesnt mean to spend every second toghter. sleeping toghter at night and every once and then going to a vacation is all they need
I wonder how do you see the future of this two? I mean even if they will confess to each other or make themself sure they care in any other way (assuming that Asami for sure loves Aki), how that can make situation any better? It's not like Asami will quit his job and change his tight schedule and will have more time for Aki, or change his dominated, introverted, "I don't have time for useless things" (read: everything except bussiness and sex, including Aki's feelings) nature. And Aki will be always reckless brat, annoying to Asami and because of that not allowing to esteem him as smart equal. Furthermore after ensuring Aki can become more flirty and I don't think Asami wants that, he likes his resistance. And what about Aki friends and family? Aki never will be able to tell them the true. Also Asami will always have to pretend Aki is his pet, if he don't want to lose respect in milieu and want to avoid enemies get revenge by using Aki and jealous friends offend him? So everything after that stay the same and they meet only in house very late in the evening to have sex? And Aki will live with detective behind his back forever? I don't write this because I don't like this couple, but I just wonder if maybe they are in hopeless situation, when met two very different worlds.