I wanted to know that if we have been making dua for something and it keeps getting delayed whereas all the other duas get accepted, so should we keep asking Allah for the dua that is getting delayed or leave it?

The delay me be due to number of reasons:

1. What you are asking for is not in your well being
2. Allah loves to see you praying and making duas always
3. Your sins are being forgiven by Allah.

You should not stop asking Allah. Instead say: Yaa Allah if you think is good for me, grant it