In order to answer this question, one need only look to the Word of God. Anything outside of the divinely given instructions and commands is superfluous to the discussion being based solely on the emotions, intellect and wisdom of man. Therefore, let's look to the infamous passage in which the Christ gives the one and only exception to the rule of one man, for one woman, for live - Matthew 19:9. In answering the questioning of the Pharisees to Jesus, namely the topic of a man being able to "put away," i.e. divorce, his wife for any reason, Jesus clearly shows that the Godly principle is that individuals stay married once that have entered into that bond (Matthew 19:4-6). Nonetheless, if a couple divorces and plans on marrying other people, He explains that the breaking of the marriage bond must be on the grounds of "fornication (Matthew 19:9, KJV)".
With this comes the inquiry of what falls under the realm of "fornication"? Strong's defines the word translated such as that which is done of a harlot (i.e. a prostitute). In light of an understanding of the principle revolving around prostitution, one should be able to get an idea of whether or not the watching, or any other use of media to reach physical gratification (i.e. listening to or even reading), of pornographic material falls under this distinction. Dictionary.com defines "prostitution" as "a woman, or man, who engages in sexual intercourse for money". So, even the English dictionary points to this "fornication" being a literal, physical, imbibing of the sexual desires outside the realm of marriage.
But, what of the passage which says "But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart (Matthew 5:28, ESV)"? That can quickly be addressed with yet another Greek word and definition. You see, the Greek word translated "adultery" is not "pornea," from which we get fornication in Matthew 19:9, but is "moicheuo" or "to commit adultery," which is the derivative of another Greek word meaning "apostate: - adulterer." It is interesting that the phrase used by the Christ in the preceding verses to His first explanation of marriage, divorce and remarriage in the eyes of God used this term instead of the one for the physical intercourse between two individuals outside of the realm of marriage.
Therefore, it is safe to say, and even Biblically accurate to say, that, while looking at an individual to lust after them is an apostasy from the marriage, it is not the breaking of the marriage bond which is defined as fornication. So, no, an individual who catches their spouse using sensory stimulants in order to achieve physical, sexual pleasure, is not Biblically able to be remarried should he break that marriage because of that sin on the part of his spouse. Even though that individual has apostatized from the godly marriage they might have once enjoyed it should not be understood as a freeing act which would allow the innocent to be married to another but rather should be worked upon so as to save the marriage before actual fornication occurs. Remember, "what God has joined together, let not man separate (Matthew 19:6, MKJV)."