That is tough situation and a very hard one for you chap. I know the feeling chap, as I to have feeling for a Lady I met, and she too is in relationship with her boyfriend.
But why do we fall for Lady who is spoken. I know how it feel. Pure torture and your mind think of her 24/7, which you wonder how she is. You believe and feel, she only Lady you want and who is best looking Lady in the world. She just make you feel alive and full of energetic to live each day
You can't sleep at night think and dream of her, to which it get you down and sad, because she someone else there in her bed cuddling up with her at night. But I wouldn't be in relationship with her, unless she happy to leave her partner. Which wouldn't be fair on him also.
But answer is no. Because of the kids, as they need their father also in their life. And it would destroy their little happy world of mum n dad, which would feel wrong.
But it going to be torture and nightmare for you now, every time you see her in your life. But how does she feel about you chap....?
This might help