But  The Greek word translated as "but" joins phrases in an adversarial way. Since it always falls in the second position, translating it as "however" often captures its feeling better. When used in writing, it creates complex sentences, but when spoken, it makes a good pausing point so that an important or humorous word can follow.

I --  (MW) The pronoun "I" is used here. Since, as the subject of the sentence, it is part of the verb, its explicit use accentuates who is speaking "I." Saying "I myself" captures this feeling in English.

say -- The word translated as "say" is the most common word that means "to say," and "to speak." When used with an object is has the sense of "call by name." . It also has many ancillary meanings such as "to count" ("to number" or like we might say, "to recount" a story) or "to choose for yourself." Christ usually uses this word to refer to his own speaking or teaching.

to -- This word "to" comes from the dative case of the following word that requires the addition of a preposition in English, but the translator must decide which preposition to use: a "to" as an indirect object,.

you, The Greek pronoun "you" here is plural and in the form of an indirect object, "to you," "for you," etc. 

That -- The word translated as "that" introduces a statement of fact or cause, "for what," "because," "since," and "wherefore."

missing "all"-- (MW) The untranslated word "all," "whole," or "every." Appears here. The sense is "every" to the following word meaning "one."

whoever -- (WW) The word translated as "whosoever" is the Greek definite article, which usually precedes a noun and, without a noun, takes the meaning of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more.  The sense here is "one" to the above "every."

looks -- (WF) The verb translated as "looks" means "to see," "to look to," "to look like," "to beware," and "to look for." It is the more tangible sense of seeing, such as seeing what is right in front of you rather than understanding so  "watch" works better.  The form is not an active verb but a participle, so "watching." With the previous article,  "the one watching." "Look" does not work as well because it doesn't take a direct object and this word does.

on -- This word is not on the source, but the verb "look" is not transitive so it requires a preposition.

a -- There is no indefinite article in Greek, but when a word doesn't have a definite article, the indefinite article can be added in English translation.

woman  -- The word translated as "woman" is  the Greek word that means "woman (as opposed to man)," "wife," "spouse," "mortal woman (as opposed to a goddess)," and "female mate (among animals)." It is in some ways closer to our "female." 

missing "for the purpose"-- (MW) The untranslated word "primarily means"towards" with verbs of seeing and looking. It also means "by reason of (for)," and "against," and several other types of "before."  Here, however, that preposition is used with the meaning of "to the purpose of" or "to the point of."

missing "the"  -- (MW) The untranslated word is the Greek definite article, "the," which usually precedes a noun and, without a noun, takes the meaning of "the one."  Here, however, it is used with an infinitive, which makes it act like a noun describing the verb's action. In Greek, infinitives work like verb forms ending in "ing" (gerunds} in English.  The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more.

to --   This "to" is added because the infinitive form of the verb requires a "to" in English.

lust   --  (WW) "Lust" is a Greek verb that means "to set one's heart upon," "to desire," "to covet," and "too long for." The verb indicates heat and passion, but not sexual passion (see this article and the reference to thumos, the root of this word.)  Jesus uses this word five times, always in reference to hunger and thirst except for here. The form is an infinitive uses as a noun describing the action, so "the craving."

after -- This word is not in Greek but it is added because the word "lust" doesn't take a direct object as the Greek verb does.

her - The word translated as "her" is the Greek word commonly translated as pronouns in English.  The word means "the same" when used as an adjective.

has -- (WT) This helping verb "has" indicates that the verb is the tense indicating an action completed in the past. This is not the tense of the verbs here, which is a point of time, past, present, or future.

committed adultery ​ -- The  Greek verb translated as "commit adultery" means "to debauch a woman" that is, to degrade a person by having sex outside of marriage. The concept is used more broadly to mean degrading people in general, specifically by encouraging them to break their vows.

with -- There is not "with" in the Greek source but it is added because the Greek verb used above takes a direct object but the English phrase includes an object.

her -- The word translated as "her" is the Greek word commonly translated as pronouns in English.  The word means "the same" when used as an adjective.

already -- "Already" is a Greek adverb meaning "by this time," "forthwith," "after," "immediately," and "now." It means proximity in time, but also place.

in -- The word translated as "in" also means "within," "with," or "among." With the accusative, it means "into," "on," and "for." When referring to time, it means "during."

his -- The word translated as "his" is the Greek word commonly translated as pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there." This pronoun follows the noun so "of his."

missing "the"  -- (MW) The untranslated word is the Greek definite article, "the." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more. 

heart. -- "Heart" is the Greek word that means "heart" both the physical organ and as the seat of emotions, which we discuss in a larger Greek context in this article here. However, this phrase can be read as defining the "heart" and both the "soul" and "the mind." The word for "heart" means the physical heart, but also the components of being human that feels the desires and creates motivation. The Greek concept is "chest," which is the root of the word translated as "lust." More about the heart and its relationship to the other components of being human, as defined by Jesus, in this article.