No sex for eighteen months isn't a small matter, in Islam a woman is perfectly within her rights to divorce over that, infact she can divorce for simply not being attracted to her husband. In practice, Muslim women very rarely initiate divorce at the 'drop of a hat.' Infact usually the opposite is true, often they tend to stick around too long whilst they often get beaten, humiliated etc. 'for the sake of the kids', society, having nowhere to go etc.
Au contraire, whatver you're saying holds true only for middle-calss (and not way too much educated or "enlightened") girls back home in Pakistan.