Peter Cumming, 58, killed Glasgow University worker Lynda Brown in the home they shared in Mannering Road, Shawlands, Glasgow.
Cumming stabbed the mother-of-two last September.
The High Court in Glasgow heard Cumming had convictions for domestic abuse towards Ms Brown.
Cumming admitted murder and will get a life sentence. The number of years must spend behind bars before being eligible for parole will be determined by judge Lord Bannatyne next month.
The court heard Ms Brown and Cumming had planned a dinner party and invited two friends, Trevor and Rosemary Clarke.
When Cumming returned after buying ingredients for the meal he claimed Ms Brown told him she had already eaten and this made him "really angry."
Cumming said he and Ms Brown had words and added that "something snapped".
He said: "I was behind her in the bedroom and I had the knife and I don't know where it came from. I was out of control.
"It's just not like me I am so in control. I need to keep things in control."
Cumming alleged Ms Brown reacted to his anger by goading him and said he picked up a large kitchen knife and plunged it into her.
He said he stabbed her once while she was standing and then once more as she lay on the ground. But a post- mortem revealed she had been stabbed four times in the back.
The fatal wound went through Ms Brown's neck, severing an artery and causing massive blood loss.
I was behind her in bedroom and had the knife. I was out of control