Piano Forum

I think you might be confusing slurs with ties.  The symbol (a curved line) is the same for both, but they function very differently.

A tie always connects just two notes of the same pitch.  It increases duration, i.e., the notes are played as if they were one note having the combined value of both notes:

https://en.wikipedia.org/wiki/Tie_%28music%29

A slur, on the other hand, encompasses two or more notes irrespective of pitch.  The duration of each note within the slur is unaffected, but they’re played legato:

https://en.wikipedia.org/wiki/Slur_%28music%29

The piece in question contains both ties and slurs.  At first glance, I thought that the D♯ you ask about in bars 7-8 was a tie because it connects two notes of the same pitch.  However, the first D♯ is a dotted quarter note; in order to be tied to the following D♯, it would need to have a value that lasts right up to the next D♯ for the two occurrences of D♯ to be held continuously as though they were one note.

But it doesn’t.  The first D♯ is held only until the E is played, and then D♯ is played again simultaneously with the F♯ at the start of the next measure.  The symbol in this instance is actually a slur rather than a tie.

Sorry this answer is a bit longer than I planned, but it's an unusual case.  In most instances the distinction between slurs and ties is much clearer.