missing "and"  -- (MW) The untranslated word "and" is used as the conjunction "and," but it also is used to add emphasis ("also"). In a series, it is can be translated as "not only...but also." After words implying sameness "as."

now - The Greek word translated as "now" means "now," "at the present moment,""presently," and "as it is."

I -- This is from the first-person, singular form of the verb.

have -- This helping verb "have" indicates that the verb is the tense indicating an action completed in the past.

told - The word translated as "speak" means "to say" and "to speak." It is one of the two most common words translated "speak," "say" and "tell," but it has more a sense of addressing and proclaiming.

you -- The Greek pronoun "you" here is plural and in the form of an indirect object, "to you," "for you," etc. As the object of a preposition, this form implies no movement, but in a fixed position or events occur at a specified time or while the action was being performed.

before  - "Before" is an uncommon Greek adverb that means "before", "sooner", "formerly," and "hitherto." Jesus only used it four times. This verb means "until" with a finite verb and "before" with an infinitive. Here it is used with the infinitive.

it -- (IW) There is nothing that can be translated as "it comes" in the Greek source.

happens, --  (WF) The word translated as "happens" means "to become," that is, to enter into a new state. In Greek, especially as used by Jesus, it is the opposite of "being," which is existence in the current state. When applied to events, this word means "to happen," "to occur," or "take place." The form is an infinitive, not an active verb, but after the "before" it acts more like a gerund, "happening."

so that -- The word translated as "so that" is a conjunction that starts a subordinate clause  "that," "when," "in order that" or "because." -- The word translated as "there" is an adverb "in that place," "there," "where," or "when."

when -- The Greek word translated as "when" introduces a phrase that explains a certain condition so "whenever" or "since."

it -- This is from the third-person, singular form of the verb.

does -- This English helping verb is used to create questions, commands, negative statements, and smooth word flow in translation from Greek

happen , -- The word translated as "comes to pass" means "to become," that is, to enter into a new state. In Greek, especially as used by Jesus, it is the opposite of "being," which is existence in the current state. When applied to events, this word means "to happen," "to occur," or "take place." The form is something that "might" happen, which is assumed in a "when" clause.

you -- This is from the second-person, plural form of the verb.

will -- This helping verb "will" indicates that the verb is the future tense. Helping or auxiliary verbs are needed to translate the Greek verb forms into English.

believe. -- The Greek word translated as "believe" does not apply to religious belief as much but trusting or relying upon other people, especially their words. Jesus usually uses it in contexts, such as the one here, that apply to trusting words.