You normally don't give out personal details of living people on the Internet, especially embarassing ones. Don't chastise yourself too severely; a lot of fatherless children do exactly what you did. I read GenForum posts when I'm not in the mood for crosswords; I'd say one or two out of 100 are like yours.
You just told the world your parents didn't get along, you are young, and you have an empty spot in your heart. If you get a message from someone saying he is your half-brother or long-lost cousin, be suspicious, especially if he asks for bus fare so he can come to see you.
has 21 people in the US with the surname Aaserude and a listed phone number. If you are an Australian, this won't help. (Don't post your home town.) If you live in the US, have a cheap long distance plan and your mother's permission, you could call 5 a week, on Sunday when the rates were low. One of them may be related and know something.
Your own birth certificate may tell you how old David was at the time and what state he was born in, which would narrow down the possibilities. I estimated the 1949 - 1973 in the heading from the fact he was probably at least 16 and less than 40 when you were born in 1989.
I hope this helps. It isn't much. You usualy have to get to people born before 1900 to find a lot of genealogy data on the Internet.