To add to Dee (thumbs up), this use of verb-ing is known in grammar as the gerund, and it acts as a noun in every way. If a preposition attaches to another word, it is always a noun or a gerund. e.g. I am thinking about football. I am thinking about playing football.

Hi, Bruno, Yes, when a verb follows a preposition, the verb must be in the -ing form. I'm tired of waiting for him. She concentrated on completing the project. He's really good at listening to others. I hope this was helpful.

The only exception to this rule is the preposition 'to'. 'To' is often part of the infinitive, for example 'I want to go' or 'He decided to leave.' In other cases, 'to' acts like a normal preposition, and is followed by a gerund (+ing form). For example, 'I'm looking forward to seeing you' or 'I'm used to working hard.' All other prepositions ( on, by, with, from, of etc) are always followed by the gerund (+ing) form of the verb.

I am sick of studying, whats up bruno?