A good first step is to get a book called cupids poison arrow-or go to its website -reuniting. This will give you the background on why things start with a burst of flame and fizzle out over time.
Ultimately what you need to do is to boost the level of non sexual touch going on.
Touch her casually on the back when you are walking past. walk up to her from behind when she is seated then steal a kiss on her ear and walk away-not waiting around for a result- massage her feet. Take Clarets suggestion for a massage SPA but you provide the massage(non sexual) in your own home. Compliment her regularly.
You will be doing the type things you did in the early part of the relationship that you did without thinking- but stopped doing over the years.
This type of behaviour will have to go on for weeks so that you build her Oxytocin levels to the point where she will be thinking of sex.
This does take work but you will get other benefits yourself. When the sex does pick up - dont make it about seeking orgasms but about getting more bonded.
Do some of your own research about Oxytocin on Google-
It is high in the early part of a relationship- I think that having high levels of it makes women more interested in Sex and it makes men into better communicators both with word and their eyes. Once it is working you will start making better eye contact with her ( and possibly with women in general) and she will have more interest in sex with you( but may be more interested in men in general as well)
Give it a try- start slowly.

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