Hello DarkJohn, and welcome to a2k
Your feelings towards your ex girlfriend are perfectly normal. I assume
she was your first love (considering your ages) and one rarely forgets
the first relationship, always will have fond memories of it, but reality is,
times have passed and things would never work out again - it's like sour
milk that won't become fresh again, no matter how long you wait.
Keep her in your good memories, and you always will have a soft spot for
her in your heart - just don't pursue a relationship again, regardless if
it's just a friendship or not. Your feelings towards her are still too raw
to appreciate a simple friendship.