Naw Riku will somehow fail or will ignore her feelings for him like he did with Shizuku and Umimi both. He honestly deserves to be forever alone. I can guarantee you Before Shizuku, and what's his name started going out. Shizuku was throwing tells towards Riku for a long time, but Riku being Riku failed to notice any of it, and failed to take action. He will fail again.
Riku not reciprocating certain feelings because he wanted their friendship dynamic to stay the same doesn't mean he should be alone forever. Yes, he had feelings for Shizuku (he also has extreme self esteem issues). Yes, he was not fully aware of her feelings for him. Yes, he inadvertently got Umimi to like Takt. No, he never saw Umimi in that way. Does Umimi like Riku more than Takt? Yes. Will Riku see new girl as a love interest? Probably not but nobody knows at this point.
Does this entire situation/premise suck? Absolutely. Is all of this completely Riku's fault? No.
It's taken about 20 some chapters but Riku has decided to take a step forward and express his feelings regardless of Shizuku's and Takt's current relationship. We are also waiting for Shizuku to explain why she is being like this as well. If it was simply her liking Takt more than Riku, Riku (as well as us - the audience) would not being going through all of this drama right now lol.
Why are Shizuku and Takt in a relationship? Why is Shizuku going all in on Riku desepite her relationship with Takt?
Those are the million dollar questions that nobody has the answers to right now.