Mr Pow told Winchester Crown Court Turner had threatened him with a hammer in Kloots nightclub, Bournemouth, just two days before Emily's death on May 7.
He said: "He kept wanting to show me the hammer.
"He kept trying to get me to touch it, which didn't look too good in the club. It was by his crotch.
"He also said his friend had a gun.
"It was like he was trying to say 'I'm a crazy person.' He was trying to make himself look like a threatening person.
"I never took it too seriously."
Mr Pow said he told Turner he wouldn't pursue Emily if she was his girlfriend.
Turner then urged Mr Pow to text Emily that evening saying he wasn't going to take her out.
Mr Pow said: "He kept asking me to text her. I just wanted to leave and carry on with my night so I just said text her whatever."
Emily replied to the text the next morning, asking what it meant and Mr Pow explained his confrontation with Turner.
The court heard she replied to his text, denying Turner was still her boyfriend.
In a text sent the night before she was discovered dead she said: "He's (Turner) fucking crazy. I will have to get a restraining order."
Later he received another text from Emily's phone, which had been allegedly written by Turner himself.
He accused Emily of being a 'lying bitch' and said he was back with her.
The court heard Turner had sent a text message to friend Dominic Birtles, 18 , the night before Emily's death accusing her of cheating.
The message read: "She lied to my face about everything.
"I will not sleep until I fuck her up.
"We said we would be honest with each other. She's trying to make herself out like the victim and me the crazy bastard."
Jurors also heard from Liam Costello who said Turner had been 'obsessive' with previous girlfriends.
The 21-year-old school friend said Turner would often talk about the number of women he had slept with and would become 'pissed off' if they broke up with him.
He said Turner had even broken in to the house of a previous girlfriend after they had split in a bid to see her.
He also allegedly threatened to kill her by sticking a pillow over her face.
He said: "He was quite obsessive. He would talk about them (girlfriends) quite a lot.
"He would talk about shagging them and he would get pissed off if they left him.
"He kept going to the house of one of his exes and tried to break in to see her.
"He said if he ever saw her he would suffocate her with a pillow."
Mr Costello said Turner had become 'pretty agitated' when his relationship with Emily broke down.
He said: "He said 'I will kill her. I might get ten years but when I come out I will still be a millionaire."
On the Friday night before her death Mr Costello said Turner ranted about Emily's clothes and had called her a slut.
He said: "He was annoyed about the dress she was wearing. He said she looked like a slut.
"He said if any guys went near her we had to kill them. He wouldn't let anyone go near her."
The trial continues tomorrow.
