Ade,
Quite a few things came to heart as I read your words, but first, what has she said about your sexual relationship? What is her side? While there are some biological reasons for a decreased sex drive, there are many more situational stressors that diminish it. Perhaps she has some emotional need that is going unfulfilled?
I noticed you said “I want a lover” as contrasted with “I want her”. Perhaps if you find out her need, you will find your own.
With warmth,
Matt