I would ignore any advice that suggests you lower your standards to be honest or those trying to blame you for everything. There are a lot of time-wasters and players in the world of online dating...
Maybe the best thing is for you to make sure you are not only dating one type of guy (the really handsome, confident, outgoing and successful ones) and give a bit of a chance to those who might not be as extrovert and outwardly successful at first glance but in fact has a lot to offer.
That does not mean dating someone you don't find attractive, maybe just remembering that sometimes it takes a bit of time to getting to know someone and develop attraction.
You should also not settle for casual sex if that is not what you want. It is perfectly fine to wait to know someone a bit more. You will weed out the lazy, casual sex seekers that way who will disappear after a couple of dates but equally there is never a guarantee that anyone will stick around after you have sex with them.
But I think there is also a point about understanding that because someone has had sex with you once they don't owe you a relationship either. You might have sex with someone a couple of times and then realise that actually it is not that great and there is no real physical compatibility. I think that is why having sex is also an important part of deciding if someone if long-term material or not.
I would also keep dating several men at once rather than focus on one guy until you find someone where you are both certain that you are compatible. It will feel less pressures if you have options and men do this all the time...