Slater was sentenced to 51 weeks in prison, suspended for two years, a two-year supervision order and 120 hours of community service.
The couple were drinking wine at his house when she came across a message on Facebook that she did not like, the court heard.
She almost instantly hit him with a glass and threw a laptop across the room.
He rushed to the shower to try to wash the blood off and she then drove him to hospital.
In hospital she first claimed that he fell down the stairs but later admitted what happened, the court was told.
Judge Toby Hedworth said: "I have listened carefully to the account and I have to say that drink played a greater role than is now suggested.
"I also take into account the affect of your actions on Mr Aitken. All that he has ever sought in these proceedings was an acknowledgement of what happened."
Owing to the time he spent in hospital, Mr Aitken lost his business and modelling career because of his injuries, the court heard.
Mr Aitken said: "It has been life-changing; my whole life changed from that moment. She wanted to come back to my house, so we did and we were cuddling but she saw a Facebook message and found something she did not like.
"Next thing I knew she swung round and hit me with a glass and my face began to pour with blood.
"I really did not think she was capable of something like that. We are not speaking to each other now, but there's so much to say.
"I still love her and I want to know why she did it. It's a really sad love story. We did not plan our future like this. Instead of us breaking up, we have been ripped apart.
"It was an act of stupidness from her and she has caused a lot of damage."
Slater, a bar promotion worker, was part of girl band Quantro but they were thrown off the ITV talent show when the attack came to light.
She was initially charged with the more serious offence of wounding with intent, but her plea to the lesser charge was accepted by the prosecution.