There are lots of opinions here, but that's all they are, opinions of what others think might be the problem if it was with their own relationships, with all their own hang-ups or fears. The one thing that occurs to me is that toohot currently has an issue about how much sex she wants compared to how much her husband wants and she doesn't know why there's a difference. She says her fantasy is having sex with another woman, that she's done it before and her husband is ok with it. What if he's not, but was afraid to say so? I could go on, but it would only be MY speculation on a variety of reasons for her problems.
As others have said, she needs to talk to him about it, and about the porn, but if he's like a lot of men, even though he may rationally think porn is ok for him to watch, he may just feel guilty about admitting it. My wife and I used to watch porn and read porn mags together (this was the days before the Internet, so we had to hire video tapes of the stuff, and it was very tame by today's standards.) It gave us new ideas for things to try out. She had a couple of fantasies she wanted to try, one of which was to make love on a mountain top somewhere, and we did that in the Lake District once.
Over time, our sex life dwindled, and I tried to discus this with her, but it's not easy to open up about what your problems are, even if you actually understand them. She just lost interest and didn't want me pestering her, but she either doesn't know WHY she lost interest, or won't admit it to me. Maybe she didn't want to hurt MY feelings. I still watch porn and I masturbate, which is my way of coping with no sex in an otherwise good relationship. I don't know if my wife knows about this as we never talk about sex now, and I don't want to upset her. I know she read '50 Shades..' She made no secret of it, but she still has no interest in sexual activity. The book was just entertainment.
So toohot's husband may feel threatened by her fantasy, he may have others himself that he's afraid to tell her about, or it may just be one of those lulls that happens in relationships, or it could be something entirely different. She says that she'd understand if he masturbates. It's easy to say that, but he may feel guilty about it and not want to admit it, for a variety of reasons.
Unless they can talk honestly about it, no one's ever going to know what's really going on.