It isn't normal. 

Now normal and abnormal are two words you'll hear a lot in dialogues between earth and fire.  Normally - whatever that is - is safe, stable, a measure by which earth can organize its reality.  Abnormality is sickness.  To fire, normality is a bore - who wants to be mediocre?  Abnormality is simply another word for individuality to fire.  Each secretly fears and desires the opposite.  Earthy people would like, once in a while, to be perfect lunatics.  And fiery people would like, once in a while, to be drearily ordinary. 

Because he bases his reality on what is in front of him, the fact that a partner is physically present, that a marriage actually exists, means that a relationship exists.  All that stuff about 'something missing' is pretty incomprehensible to the earth signs.  Duty. Loyalty, responsibility, commitment and security are much more important than wild romantic idealism.  The subtler nuances of relating often escape him.  Tragically, his partner often escapes him as well, seeking more of the chaotic burning stuff of spiritual passion and soul.  It is fire who will usually abandon a relationship with an earth sign, unless the fire sign has one affair too many and the earth sign leaves out of wounded vindictiveness. 

Sexual problems per se do not often afflict the earth signs.  Inhibitions about fantasy do, though, they tend to be a prudish lot when it comes to the more exotic aspect of erotica.  They appreciate the senses, not the imagination.  You can imagine where this leads.