How can you tell before you sleep with someone if they are looking for a relationship or just a one nighter?

i have dated a few girls and some of them were very touchy on the first date and brought me back to their room. i found it a bit promiscuous so i slowed it down. after the third date they stopped wanting to date me because of how slow i slowed it down. how can i tell before i sleep with a girl if she wants to be more then just a one nighter. also does this girl sound like she likes me? their is this girl in my cl i met a month ago. the first cl i talked to her in she walked out with me and talked to me for a while. when i would see her at the dc's she would talk to me often but also seem to time it when her bf was not around lol. i recently sent her an email asking if she would like to get together (i noticed she is single now and broke up with her bf) the message asked her if she would like to get together sometime she replyed sure and without me asking gave me her number. does it sound like she likes me?