Hola Johan
In this sentence:
The subject of the sentence is "what is bothering you" (que veas a ese chico) so verb molestar needs to agree with that; in this case, as it is an idea, we can say that "que veas a ese chico" would be "it". The verb then needs to agree with "it"which is the 3rd person singular. Let's change the sentence slightly to:
You can see here that:
Eso = subject
molesta = verb (agreeing with the subject)
me = Indirect object pronoun
All these "inverted" verbs in this lesson work the same way. The structure doesn't coincide with the English structure as in English it is a straight forward sentence with the normal order: Subject + verb + indirect object
( That + bothers + me), but in Spanish the order is inverted.
I hope this explanation helps,
Saludos
Inma