I have a problem understanding this:

çünkü birine verebileceğin en büyük acı,aşık olmadığın birini kendine aşık etmektir.

,,,this "aşık" is giving me a headache.If it were "aşk" I´d understand this as:because you can (are able to) cause(give) someone the greatest pain when not giving back( returning)love you´re recieving( is given to you by this person).

text in full is:

Sevmediğin birine asla"seni seviyorum" deme.İçinde olmayan duygulardan varmış gibi söz etme.Kimsenin hayatına kalbini kırmak için girme.Sevgi dolu bakan gözlere asla yalan söyleme.Çünkü birine verebileceğin en büyük acı,aşık olmadığın birini kendine aşık etmektir.

my understanding:never say"I love you" if you don´t love.Don´t make promisses if there are no feelings.Don´t enter someones life to break their heart.Never lie to the eyes who are looking at you full of love.Because you can give ????????

My Try:

That is because the greatest pain you can give to someone is that a person who doesn´t love her steals her heart.

The dictionary gives kendine aşık etmek ´to sweep someone off her feet, to steal someone´s heart´.

But...in my opinion just like there is something wrong in the syntax of the last part. Of course I am wrong but I would feel better if it was

                        aşık olmadığının birini kendine aşık etmesidir

Maybe someone will come and explain it for us.

thank you very much Abla!

I´m happy to see that my understanding wasn so much wrong go me!!

I got it now. The equivalent of an English relative clause where the relative pronoun is the object:

                  who you do not love > DIK participle.

So simple when someone just opens the knot. Thank you, tunci.

Içinde olmayan duygulardan varmış gibi söz etme.

 Please can someone tell me why -dan is present here? Thanks. 

The verb "Söz etmek" is used with ablative case " -dAn söz etmek" [to tell about something to someone, to talk about something,to mention something to someone]

Ona bundan söz etme. --> Dont tell [mention] her about this.

Therefore, the english correspondence of it [in this case] would be "about"

I should have known that...Hızlı cevabın için çok teşekkür ederim Tunci.