Is it wrong to fall in love with a married man?

I am in love with a man older than me,the difference between our age is 12 years. He is married and has two girls. I wasn’t intend to fall in love with him we were just friends untill I knew that he hates her and wants badly to get the divorce but he couldn’t. He asked me to marry him but I’m still waiting something to happen in their relation. I’m worried about the kids but I know that if it wasn’t me it will be someone else. We have been together for 2 years and we are sure that each one of us will die if this relation ends. The problem is that I have a guilty conscience and don’t know what are the steps to take to move on in this relation?