Mousy: Demisexuality refers to the sexual attraction that one experiences, which is not the same as libido.
Libido, or sex drive, refers to a physical desire for sex. People of any sexual orientation can have any level of libido.
For example, it is possible for an asexual person to have a high libido, which would mean that the person is not attracted to anyone but experiences the physical desire for sex. In this case, the desire is not directed towards anyone.
A person who has a low libido but is allosexual (not on the asexual spectrum) may well still experience attraction towards people, but not have the drive to engage in sexual activity.
In contrast, demisexuality refers to the experience of secondary but not primary sexual attraction, which means that one only experiences attraction after developing an emotional connection.
Note that this is not the same as “only having sex with someone after forming an emotional connection”.
Attraction and sex drive are only two amongst the many factors that can determine people’s decision to have sex (or not have sex). They may well lead to the same type of behaviour, but they are not the same thing.