Thank you for your question.
I agree with you that with him peeing too much he could be having diabetes
He can easily get himself checked by having a blood test
at fasting state for diabetes.
If his blood glucose
level on fasting is less than 126 then he does not have diabetes.
If it is between 100-125 then it means that he is having "prediabetes" or in other words he is in risk for getting diabetes in the future.
If his blood levels are less than 100, this means that he does not have diabetes at all.
However, having said all that, although diabetes can cause erection problems but that would usually require diabetes to be of long duration.
In other words usually people who have had diabetes for more than a decade tend to have erection problems rather than people who have just been diagnosed to be diabetic.
High blood pressure
should not cause this problem
The most common cause of erection problems like this are psychological problems.