Actually there's a difference between desparate and nice. There's nice as in what you are describing. They are always there for support. They are the ones that listen. And they are the ones that respect the ones they care for.
The desparate ones are the ones that push to get something. Push for attention. Get love any way they can even if it means being a doormat and letting the person walk all over them. They don't care as long as they appear to be getting the attention they desire. They get sex from a girl that coesn't give a shit about him (visa versa for argument's sake), They do errands knowing that the person giving orders couldn't care less about how they feel as long as they get what they want from the desperado.
The biggest difference is that desparate people have little to no self esteem. The nice guys still have a sense of confidence that desparados lack. Girls are attracted to confidence and self-esteem. It really has little to do with assholes unless the girl is fusked up herself with little to no self esteem. If a nice guy has the confidence he'll attract girls. If a desparado grows some balls and gets some self esteem/confidence, he too will get girls and won't have to beg for their attention. Confident girls don't like assholes and don't put up with crap from assholes cause they know how they are supposed to be treated and know they can get that from a nice guy. Also, conficent girls don't respect desparate guys. So understand this, girls are attracted to confidence and self esteem. It just gets mixed up when the asshole puts on some sort of charade that shows confidence but meanwhile is scared shitless and doesn't have a clue on how to give respect, or even make a girl happy. That's the secret. Give respect, have self-confidence and truly show you care and you'll be one of those self-confident, nice-guy chick magnets. Don't fake it cause nice girls will see right through it. Girls that lack esteem and confidence are more likely to be desparate and cheat. The don't give respect and also have no clue how to treat a guy.