My Wife's Obsession

My wife and I have been married for 30 years. I thought I knew everything about her.
Recently, maybe for the last 6 months she has been disinterested in sex.
I asked her about it and eventually she said that if I promised not to be judgmental she would tell me everything.
I agreed.
She told me that years ago she was r*ped by two guys when she'd had a few drinks too many.
She had passed out and woke up with one of the guys on top of her and the other holding her arms down. I was shocked but sympathetic and tried to comfort her.
She stopped me saying "NO, you don't understand".
She then went on to say that although she had pushed this memory deep down into her subconscious for years, the memory of it resurfaced about a year ago and the more she thought about it, the less "ordinary sex" with me excited her.
I thought it was some kind of joke but no, she meant what she said.
She also told me that she hadn't felt that she could tell me about it before because she was afraid i would kick her out. Not for being a r*pe victim all those years ago, but for having fantasies about it NOW, for the last year.
She said that sex with me had become less frequent because it didn't excite her and that she had been masturbating every day, sometime more than once a day thinking about being r*ped.
She then told me some of the things that the 2 guys did to her. I was shocked for 2 reasons, firstly because my wife was excited by being abused like this and secondly because what she was telling me aroused me and I could feel my erection growing.
She noticed too and asked if what she was confessing to me excited me sexually. I admitted that it did.
So, she asked me to r*pe her. To hold her down and do anything that I wanted to her. She said I could use her in any way that I had ever had dirty fantasies about. I could use her mouth, pussy and asshole and do anything I wanted, and not to wear a condom. She has always said no to anal sex before, so this confused me even more. As did the no condom rule, because up to now condoms had been the norm, since she didn't take any protection herself and had not yet hit menopause so was still fertile.
Although I was aroused, I couldn't bring myself to treat her like that, so she went to the bedroom in a huff, alone and used her vibrator and her imagination to satisfy her.
Although in the past, she had masturbated discreetly and in private, this time she left the bedroom door open and was not discreet about the noises she was making.
By now I am confused and conflicted emotionally. I don't want to abuse her myself, but my erection is so hard it's starting to make my cock ache.
I walk quietly to the bedroom door and she is on her back on the bed, naked. She has a belt around her throat, tied to the bed head and a vibrator in her pussy and her anus. There is a growing wet patch on the sheets between her legs and I can see a creamy watery discharge running from her pussy, down her ass crack and onto the sheet. She's got her eyes closed and she's saying things like f*ck me, do it rough, make me your bitch. And of course, R*PE me, cum in me, I'm a whore! I'm a slut!
I stood in the doorway, got my cock out and started to wank looking at her. She was thrashing around on the bed as if pretending to struggle while simultaneously thrusting the vibrators roughly in and out of both holes and in my mind I could suddenly picture the two guys double penetrating her.
This mental picture caused me to ejaculate pretty much straight away, and I backed out of sight before she opened her eyes and saw me.
What do I do now? I have no idea.
I don't want to lower myself to the level of a r*pist, but I do want to have sex with my wife and I want her to enjoy it.