Wow! Thank you everyone for such great advice.
Now to try to answer the questions...
Yes, she does know about mine and his relationship. He sleeps over at my home at least once a week. She seems very accepting of it. He will hug and kiss me in her presence and she seems fine.
I've read a few books on polyamory and I'm trying so hard not to get jealous or competitive. But I am human and working my way through such new emotions.
Yes, I guess seeing her maybe change her physical response towards him maybe evokes a competitive edge in me that I don't usually have but in all honesty, it stems from the fact that I feel she is the one feeling the sudden competition and making these advances only when friends are around or she feels threatened.
She has told him several times in the last several months that he is free to leave her, despite her critical illness, that she would forgive him and love him anyways.... but he was racked with guilt by that statement and declared his commitment to her.
I have never expected that to change. But when you are in love, there's always that slight hope.
Blackunicorn - thank you so much. You are right. I need to have faith in his love for me. I know it's genuine. And I have to stop feeling like such an outsider and risk looking too needy by expressing my feelings to him. He's always been open to listening and empathetic to my thoughts. I need to have more faith.