This is about structure rather than meaning. 'To' is followed by the base form of the verb ( live ) when the 'to' is part of the infinitive. For example: want + to live try + to live decide + to live be able + to live 'To' is followed by the gerund (living) when the 'to' is part of the verb phrase. In these situations, 'to' is a regular preposition, and ( like 'with', 'for', 'at' and so on) it needs to be followed by a gerund. For example: Look forward to + living Be used to + living Be accustomed to + living A gerund is a verb in 'noun form'. So a good way to know whether to use the gerund or not is to say 'Can I substitute this verb for a noun?'. In these sentences, you could say, for example, 'I'm looking forward to your visit' or 'I'm used to a quiet life', so that's why we use a gerund. But you can't say 'I'm able to + noun', so that's why 'I'm able' has to be followed by an infinitive, not a gerund. As you say, in most cases, 'to' + verb is an infinitive form. The use of the gerund form is more unusual, and restricted to certain expressions such as those above.

When you add ing on the end of a verb it usually represents something that is happening at that moment for example I watched a movie (This is in past tense so it doesn't require +ing instead it uses -ed) I am watching a movie (This is present tense so it does use +ing) "To watch" is the general way of seeing a verb in a text book. When adding +ing it expresses that the action is occurring at that moment. However as you said sometimes it can be said with or without the +ing such as "I look forward to it" or "I am looking forward to it" But usually if it is an action in the present or future tense it requires +ing on the end. Hopefully this helps!