Honestly, it sounds like there's some emotional issues there. Here are some generic answers for you... they're nonspecific because I don't know you.

One thing that happens in relationships a lot is that the relationship often begins with lots of foreplay... which tapers away. It should be the other way around. You need more foreplay as time goes by. Remember this important thing... for women, foreplay is when you are NOT touching her genitals or breasts. Make a point to touch the rest of her, since she is so sensitive, do it without brushing your dick on her. Brush past her sexual areas, but never touch them. Then, go quietly into the bathroom and leave her be, and have a shower and take care of your need. Quietly.

According to studies, women need 10 meaningful, non-sexual touches per day. Start keeping count. Give her a hug in the morning (a kiss if you have a hard-on, without grinding against her or rubbing on her, that's important, it tells her it's "not about sex"). Brush her shoulder after breakfast. Kiss on the cheek as you leave. Gentle caress on the back when you get home. Etc. No pressure, no sexual attitude. Simple touches.

Since she is into porn, leave some DISCREETLY hidden in your drawer. Get caught sneaking it back in, but downplay it... so she knows it's there, but you didn't MEAN for her to know! (no, really.. ). Stories are better, if you can find any. Hustler magazine, maybe. That sort of thing.

Start helping yourself out, but never do it where she can hear or might see (or if she might see, it's because she's doing something out of the ordinary... going to the bathroom in the bedroom when she is usually cooking, that sort of thing). Keep yourself "satisfied" so that when you are around her, you've just finished yourself, so you can be near her without expectation. That is important when that's her complaint.

Be careful to be romantic. Don't be sexual before, or after, you are romantic. In fact, make a POINT to not be sexual, even if she initiates. Why? Because it makes it clear "this is not to obligate you, this is to be romantic, end of story."

Hopefully, she'll start reading some of the porn and turning herself on. She'll begin to see your romance as being "romance" and not "sex." When you are already satiated when you are with her, the expectation of sex (that desperate needy atmosphere that men can get) will be gone.

Imagine that you have to "woo" her all over again. Basically, you do. Look at her like a whole new aquaintance whom you must get to know. Ask what she did today, take an interest in her... what are her dreams? What is her favorite color, is it the same still? Who is she today? Because she needs to be seen as "her" and not as "your wife" and "their mother." So get to know her again.. date her, court her. Imagine you are going to ask her to "remarry" you... Imagine dating her as if there were no kids and you were 18 again together. What would you do? Where would you take her?