What should I do about my mother

Hey Guys!   Need some advise.   So me and my mum are very close to each other. She has a deep affection for me as I am the elder of her two sons. She was married twice but unfortunately got divorced from both of them. Me and mum have had a very open relationship as we are more than just a mom son.   Since puberty I have had a great sexual attraction towards my mum. Because of her great busty body I have masturbated hundreds of times thinking about her.    Since the past 2 years my mum has become quite open in conversations with me. She told me about her bra size while on shopping which was quite awkward for me. A size 38DD when entered my ear gave me a hard on instantly. Then the other day showed me her bra and panties collection in her closet and asked me as to how they were. When we both were travelling once to another city last year, and I forgot my underwear collection at home. She gave me her panties me to wear. And i found that very hot.   Then last month when we were talking with each other. I asked her naively that do women over the age of 50 have sexual desires and if yes do they masturbate. And she openly said, yes they do, and that She too have sexual feelings and yes she is masturbating since the age of 26. With my heart beating fast, i with courage asked her. How often do you masturbate now. And she replied with a smile, that it’s inappropriate, but yea I masturbate 3 times a month and it takes around 5 minutes to get off.    She also tells me that she has never been sexually satisfied with both of her husbands but doesn’t need a physical man to fullfill her needs now after her divorce. She finds masturbation as the solution to all her needs.    I have discussed my sexual relations with my mum. As i told her I had anal with my girlfriend and she was quite fine with it. Just last week I shower her the nudes of my ex and she commented that they are one horrible looking boobs :p. She knows i am a fan of big boobs and she sometimes teases me by saying “look at your aunt, she has big boobs, do you masturbate by thinking about her?”   She has seen my dick a few times as I have roamed naked in my room while she pretends to lower her eyes but somehow keeps an eye on my bulge and even I have seen her tons of times in a towel after she comes from the shower. As mostly i am sitting in her room after she comes from the shower.   Though I still masturbate to this day by thinking about her. But I feel its wrong.  But then all the dirty talk makes me feel very horny.   Is it normal for a mother and son to talk like this? Does this happen? Does she want me? How should I go one step further? Should I back out? If yes, then how?   This all comes from a culture which is very conservative.   I’ll love to see what you guys respond with.