Complex situation

So for the last couple of years now I've been having sex with the guy of my dreams. We've both confessed we really like each other and we find each other attractive.
The issue is, he's in a relationship and has his own house with his girlfriend. They've been together for over 7 years. He's not happy with her but doesn't want to leave her because they've got too many ties and the repercussions of leaving her would be huge.
Before anyone says "you shouldn't be getting. Involved with a man who's in a relationship" believe me, I know. 
He's my soulmate though. He's my best friend and we have such an amazing connection. He's even said that. I've spoken to him about how it's not right for his girlfriend and how they should split but he is too scared to do it.
Does anyone have any advice at all?
Thank you everyone