The 58-year-old author of titles such as The Trick is to Keep Breathing, Foreign Parts and Blood was allegedly subjected to threats and abuse by Graeme McNaught.
Mr McNaught, 54, a world-renowned concert pianist, is accused of leaving letters and parcels at the home Ms Galloway shares with her husband Jonathan May and friend Alison Cameron in Uddingston, South Lanarkshire, after their six-year relationship ended.
Mr McNaught went on trial yesterday after pleading not guilty to 10 charges at Hamilton Sheriff Court.
Ms Galloway and Mr McNaught, of Mount Vernon, Glasgow, met in 1990 and had a six year on-off relationship during which they had a son, James, now 22.
Giving evidence from behind protective screens, Ms Galloway told a jury she had called police in January 2012 after discovering a suspicious package signed by Mr McNaught had been left in her kitchen.
She told the court: "I had no idea what it was but I knew very quickly who it was from.
"It was wrapped in paper and it had drips of wax on the strings which looked as though they had been laid out in a particular pattern. It was in Graeme's handwriting and it looked quite intimidating.
"The thing that worried me the most was that someone must have come in the back door and put the parcel in the kitchen. I found that quite disturbing because we have had some pretty erratic disturbances over the years."
Ms Galloway said she had received a number of "bizarre" letters and parcels containing drawings and paintings from Mr McNaught since their break-up in 1996.
She said: "All of them had an intimidatory nature and they were quite bizarre and unsettling. The letters would say things like I was being watched and people knew what I was doing. The drawings could be eyes staring at you or images of fire. There was something almost ritualistic about them.
"We would get things from Venice, Holland, wherever Graeme had been, we would get these items in the post.
"It makes your blood run cold every time it happens. I was very upset and frightened.
"When it happens repeatedly it starts to creep you out and it is overwhelming if you have tried everything in your armoury to put a stop to it."
Under questioning from depute fiscal Imran Bashir, Ms Galloway described her unconventional relationship and said it had been strained since 1991.
She added: "When I fell pregnant he was not impressed by the idea. He seemed very nervous and certainly apprehensive.
"I remember him using the phrase, 'There is no we'."
Ms Galloway summed up the relationship as having "romantic overtones."
Mr McNaught is charged with repeatedly turning up at the author's home and banging on the door demanding to be let in.
He also allegedly claimed to be "King of Scotland" before he threatened to "walk into water" with their son. He is also accused of following Ms Galloway in Edinburgh while screaming and swearing at her in 1997.
Ms Galloway's first novel, The Trick is to keep Breathing, published in 1990, is considered a modern classic. It was shortlisted for three awards, including the Whitbread for first-time novelists. Foreign Parts, her 1994 second novel, won the McVitie's Prize and she has also received the EM Forster Award.
The trial continues.