Commitment Sex 

When neither person in a relationship (boyfriend, girlfriend, etm.) wants to engage in sexual intercourse, but thinks the other wants "it".

commitment sex sucks

Commitment Sex by LATNIO-POWER June 6, 2011

Non commitment sex 

When you have sexual intercourse with someone without knowing whether or not you want to be in an active relationship with said someone

Omg I just had non commitment sex with that hot guy John

Non commitment sex by Sickasfrick August 30, 2015