if they don't want to be around you like coming up with excuses not to meet you somewhere or to be around you then they don't like you anymore
Go to the guy and tell him to tell his girlfriend that he has a crush on you and that he thinks they should get over each other.
Move on find another guy
if they loose interest in you
forget him or make him admit it
if he doesnt flirt with you 24/7 then he doesnt like you...(=
tell him you need a vacation or should go out more often
If he doesnt talk to you, takes no notice of you, then he doesnt like you. :(
If you are apart and he behaves "like he doesnt love you anymore" then it is over and the relationship isn't "salvagable"
tell him you dont like him anymore
tell on him or not like him anymore
ask him
ask him if he would have a threesome with you and another guy and if he goes for it then he doesnt really love you anymore