来不及爱你 Too late to love you
The break down:


「來」(come ) 
「及」implies 「及時」 (in time) here.
「得」or 「不」 are the two potential particles that indicate " "able , or "unable" 

*You either able or unable to come in time.  That's why they are called potential particles.


In summary:

「來」 (come) 「不」(unable to) 「及」 (in time ) 

「來不及」= unable to come in time = too late

「來不及愛你」= unable to come to love you in time = too late to love you.