1. The gerund: watching
A gerund is a type of verbal that acts as a noun in a sentence, thus, it can be a subject, a direct or indirect object, an object of a preposition or a predicate complement. It is formed with the root of a verb + “ing,” like “watch” + “ing” = “watching.” In the sentence, “watching” is a gerund because it is the direct object of the verb “loved,” that is, it is the noun receiving the main action.
2. The infinitive form of the verb “watch” is “to watch”
An infinitive is a verb form consisting of “to” + the root of a verb (E.g. to watch, to be, to connect), and which can be used in many situations and after certain verbs like love, want, hate and like.
3. Sentence with the infinitive:
Debbie loved to watch the skaters glide around the rink.