Love language

What does it mean if you can’t figure out your significant others love language? He’s a very stand-offish “I don’t give a fuck” type of person. We were together almost 4 years at one point, broke up for about a year, got back together and now he’s a completely different person. It always has me questioning if he wanted me back because he was comfortable and knew how I was, or if he still truly does love me but maybe is scared or doesn’t know how to express it.