Have any of you read this ? Which book is it?

Girls! Ladies! Mommas!
Calling each one of you.. Below is the storyline of a book I had read long back. I have been wanting to read it again, but there's a slight hitch. I remember neither the author nor the title!

It was gifted to me by a cousin while in my teens, and I loved the book. Unfortunately, one of my numerous friends borrowed it and never bothered to return it.I've tried searching the net for it, but while I've come across a play that fits the storyline almost perfectly, I'm still searching for the book. I know it exists because I've read it.If any of you recognise this story and can tell me the title/author, I would be much obliged.

The story is set in the middle of World War (dunno whether I or II) and this is what I remember of it...It starts off with this young, handsome and brilliant German scientist and this warm, vivacious, lovely lady(non-German), who are married to each other and are deeply in love, with their cup of happiness overflowing. However being a German, he is wanted by the Nazis. The couple get wind of the less than noble intentions of the Nazis and engineer an escape, but at the last minute, the husband( I think his name is Stefan) is caught. The wife is devastated. She tries to get him released, but in vain, and they are parted, him inside the concentration camp and her outside.She becomes a shadow of her earlier self, however life goes on.

Alex comes into her life. Dashing, debonair and a well -heeled Greek,, ( I forget his profession, but he is someone with a lot of political hold) he falls in love with her almost instantly, but she is devoted to her husband and rebuffs all his advances.Time passes and he manages to win her reluctant love. By this time she is convinced that Stefan would be no more, that he would have been tortured to death, for she has left no stone unturned to find out his whereabouts.The two of them become lovers. They decide to escape from this place full of memories and to get married, when she finds out that her husband is alive .

Tho a tortured wreck of his former self, Stefan is as much in love with his wife as ever, and believes her love to be unchanged. Her love for him indeed has not changed, but there is a new love to be considered. And Alex loves her, but cannot in all humanity leave Stefan there to die, while he escapes with Stefan's wife. How Alex helps Stefan and his lover (Drat, I just don't remember her name at all) escape the clutches of the Nazis, while himself falling to their bullets forms the bittersweet ending of this novel.

What I can remember of the title is that it had the words- "Love is We know of Heaven and Hell.." in it somewhere. I dunno if that was the title or just a brief note on the contents. It was an extremely well-written novel on the emotions of a woman torn between her husband and her lover. And I would love to read it again now, when I am not such an impressionable teen anymore. It had undertones of A Tale of Two Cities in the final pages- the urgency, the desperation, the relief that they've got away, but also a pang that Alex hasn't managed it...

Now, if any of you readers've come across this book, please jot down the name of the title/author in the comments. It would be such a HELP.