The boy I’ve been seeing has had a secret girlfriend all along

I know the right thing to do is tell her but I’m so afraid of losing him even though I know he’s not really a loss if that’s what he’s like but it is KILLING me.

He’s been in my life for about a year now and supported me through so much, it’s hard to come to terms with the fact that it’s all been a lie and he’s not the guy I thought he was.

I know if I was the girlfriend I would want to be told but how do I go about it?