Advice Needed: I am In Love With My Friends Ex-Girlfriend

Hello,

It happened that 9 years ago my friend broke up with his girl friend. And after that he moved on, went to the UK and got married afterwards ( he has two kids now, his wife is in the UK, he is here in Nigeria). I was a friend to his girl friend even after they broke up and maintained contact ever after though we were loosing contacts in between then. 

Fast forward to 3 months ago, we started seeing, hanging out and enjoyed each other's company, maintaining the fact that we are good friends. Of late, we both have recognized that we have got feelings for each other and love each other. She is all I want in a woman. I haven't proposed to her yet. But when I think of proposing to her, I have mixed feelings like letting my friend down. Question is? ........ 

Should I let my friend into the know? Should I go ahead and propose her or not? Advice Needed. 

 I Am Just so worried considering the relationship with my male friend cos we still hang Out

NB: Me maintaining a friendship with her caused a rusty relationship between me and my male friend, her ex-boyfriend. Though we still see and hangout when need bé. - See more at: http://www.lailasblog.com/2014/11/blog-reader-needs-your-advice-urgently_25.html?utm_source=dlvr.it&utm_medium=tumblr#sthash.0GHMFmSB.dpuf