Loss of libido can have a variety of causes – some psychological, some not. One of the leading causes of lost sexual desire is stress and fatigue. In this case the condition is temporary and desire returns when the stressful period ends, or when you’re able to get enough rest.
Anxiety
Sex can arouse a lot of anxiety in people who are unsure of themselves or fear humiliation. For someone who has never had sex – or has had a bad experience with sex – the anxiety level can be overwhelming. People may fear that they will not be able to become aroused or excited, and fail their partner. Alternatively, they may fear the consequences of sexual activity (pregnancy or sexually transmitted infections). Fear of sex – or even intimacy – is not uncommon, and most people experience it at some time in their lives.
Estrangement from partner
Someone who feels hurt by, or angry with, their partner may express their emotions through a lack of sexual desire. Women, particularly, find it difficult to have sex when their feelings have been hurt or they feel “unsafe” in the relationship. Negative feelings toward your partner may be incompatible with the prospect of sexual intimacy, which decreases your level of arousal.
Misdirected sexual desire
This phenomenon often occurs in the case of “closeted” gay men and women. While actual sexual desire may be high with members of their appropriate sexual orientation, many people ashamed or insecure about their sexuality will still force themselves to desire the wrong sex. Often “closeted” individuals marry and have children while still suffering from lack of sexual desire for their spouses. Others may be disturbed by their fantasies or fetishes and may try to ignore them by repressing their sexual desire.
Physiological causes
Not all the causes of low sexual desire are psychological in nature – in older men, it can be caused by a low level of the hormone androgen. Women may experience “interruptions” in sexual desire through different stages in their lives. Hormonal deficiency can sometimes be treated with hormone injections. Anything that adversely affects your metabolism will undoubtedly cause some lack of sexual desire. This may include an accident, trauma or illness. Depression, and the medication used to treat it, may adversely affect libido, as will anything that causes pain. You should speak to your doctor if you have problems created by medication, or if sex has become painful in any way.
I really want to want sex…
A short period of loss of desire may correct itself. Reducing stress or anxiety will help, too. If it is caused by problems with your partner, physical wellbeing or fears, see your doctor, a counsellor or even a sex therapist. Work out your fears or expectations. If you have a loving partner, talk to her or him and spend time together finding things that you enjoy, that are exciting or that make you feel closer to each other. Wanting to want you partner is a good start.
Source: Healthinsite.net
In Excess 
hello,iam engaged to lady whom iam really in love to.we have grown so very close to each other that we hardly stay a day apart, until about six weeks ago when she told me some things she did in her past which she was’nt proud of,i managed to overlook it inorder to forge ahead for the future together but the truth is that i dont really see myself sexually attracted to her anymore,but deep down,i know am very much in love with her.problem is that am beginning to nurse the idea of letting her go,due to my lack of sex drive towards her,do you think its the right thing to do now.. cheers
Sex is just one of the ingredients of love. you said that deep down you know that you love her. for her to open up and tell you of her past is clear indication of her trust in you. Please do not break her heart. just move on and marry her. do not just be driven by sex, instead let love be your drive. and by the way, some of us have pasts that are not very good but our spouses overlooked and now we are happily married and have wonderful kids
when i first got with my now husband i was warned he was abbusive. However the 2 previous wives he was with were identical. In fact became best friends. They both cheated very briefly in their relationships. they were both bad moms and bad wives. he would get angry they would hit him and full fight would be on. i on the other hand am sweet, christian tendency, lovingg, caring and good person in general. he dont HIT me but he so messed up mentally from their relationships and an extremely awful childhood. Hes a recovering alcoholic. after our first child together he became jealous of the time i spent with my son not him he became verbally and mentally abusive. 4 years later I was pregnant with second child , a girl is when it became physical. We had an argument when he tried to become intimate and i turned him down, he threw me around demandind sex. he failed. Ever since then he feels even if only one day has passed I should never deny him sex. Now that it is only done by him needing it not for me, Ive lost all sexual desire.N sex isnt everything but if u lost any of it dont push on until it can be resolved, or someone going to be very unhappy and no matter how awesome the actual experience is it will be unsatisfying. good luck to u.