1) To is always a preposition and nothing else. However, it is used in a variety of ways.
2) - I was lied to. ACTIVE: X lied to me. to me is a prepositional phrase, it is not a to-infinitive. The sentence is also passive.
- She was read to. ACTIVE: X read to her every night before bed.
In a passive sentence, as the two above, you do not need to use the pronoun if the pronoun that comes after to is understood by the speakers and the original action verb "takes" to.
To lie to **someone|| to read to someone||to adhere to something ||
3) I did that because they wanted me to. I did that because they wanted me to do that.
wanted me to = they wanted me to do that.
Certain verbs do not call for repeating the main verb. They are called verbs of emotion and the to is left at the end of the sentence without repeating the verb, in spoken English.
Need, want, love, like, hate, prefer, (verbs of emotion) and also certain others like advise or tell or ask and other action verbs (but not the verb suggest). (Sorry, I don't have an entire list for you.)
You do not need to repeat an infinitive clause if there is no auxiliary used after the to:
- You should not call me again. I told you not to [call me again].
- I prefer to leave early. Do you want to [leave early]?
- I want to watch that movie on TV right now. Do you want to [watch that movie again]?
- They told us to stop by their house. Did they tell you to [stop by their house]?
I wanted to have forgotten that by now. Did you also want to have forgotten that by now also?