I know I've struggled to tell wether or not a guy is just after sex or if he wants a serious relationship before and I'm sure there are several other girls have to. So, I thought I'd share my take on how I've learned to tell the difference.
1) He calls you last minute and doesn't make plans for a later date if you're busy. I don't think I can emphasize this one enough. If he really wants to spend time with you he will make every effort to do so, even if it's only for 5 minutes. This means he's probably never going to ask you on a proper date because he doesn't consider you girlfriend material.
2) He only calls you once or twice a week (and never on weekends). This ties in with my first point. He has reserved his weekends for people he cares about, not girls he just wants to sleep with.
3) He never pays for you. If he doesn't pay, its not a date. This obviously doesn't mean that he has to pay for you every single time you go out, but on the odd occasion (if he's not just after sex), he will make an effort.
4) You never meet his friends. The less information you have about him, the easier it is for him to ditch you. If you don't know who he hangs out with, or where he lives, or what his last name is, he can easily stop answering your calls and texts and disappear into the night.
5) He always turns the convosation to sex. Every time you talk or text, it somehow turns into a conversation about sex and he's might have even stopped being suttle about it or given up flirting with you all together.
6) He only compliments your looks. He's only interested in your appearence, not your personality. If his compliments are shellow and superficial at best he's just not that into you.
I hope this helps at least the younger girls on here!