Michael Dobbins was cleared of 10 charges last week.
Throughout the two-week trial, a number of witnesses claimed the alleged victim was “besotted by” and “adored” him.
Mr Dobbins said he intended to take legal action against the police and the Public Prosecution Service (PPS).
He was charged with six counts of rape, three sexual assaults and one charge of sexual activity with someone who was unable to give consent due to a mental disorder.
The offences were alleged to have been committed on dates between 2013 and 2015.
The woman was a pupil at Ardnashee School until she was 19.
After deliberating for just over two hours the jury returned unanimous verdicts of not guilty.
Mr Dobbins said he “felt sick to his stomach” when he first heard about the allegations.
“I’m angry at the PSNI,” he told BBC NI’s North West reporter Keiron Tourish.
“I don’t think I have any confidence left in them at all and the way they conducted themselves throughout this entire investigation. Evidence of truth was ignored.
“The PPS need to reflect on how this ever got anywhere near a court, but on one level I’m very glad that it got to a court because people can hear and understand the details of this case and find out for themselves how preposterous this was.
“If you start with the belief that one person is a victim, then the other person by default is obviously guilty, this case suffered from that.”
Mr Dobbins told Coleraine Court he knew the woman from when she was about 11 or 12 and described her as bubbly and outgoing.
But he said she had developed an obsession with him and had come over to his office too often.
He said he always adopted an open door policy at the school office.
The woman had also been to his home with another student and his son.
He said in hindsight he perhaps should not have taken her there.
The court was told the woman knew Mr Dobbins since she was a child and had a photo of him on her phone’s screen saver.
The trial heard protocols had to be put in place to stop the woman continually calling into the principal’s office.
“It’s had a severe toll, I have been put on medication for anxiety, stress, sleep disorder, depression, suicidal ideation. It’s been a very tough time.
“My father died with Covid two years ago with all this hanging over me. I find that very hard to forgive and to forget.”
Mr Dobbins now wants to know why the case was even taken in the first place when there was no substance to the claims.
“There has to be lessons learned from this whole shambolic fiasco.”Tags: