sex and marriage

Matt 19:9 - And I say to you, whoever divorces his wife, except for sexual
immorality, and marries another, commits adultery; and whoever marries her who
is divorced commits adultery.

why is this so?its like He's saying if you have sex with someone,God sees that person as your husband or your wife.So the first person you have sex with God see's them as you husband/wife.And then you break up with that person simply because "its not working".The second person you sleep with,God sees it as adultery,same applies with the third and forth etc...Blood is the most serious covernant or promise ever and there's blood involved in sex.So when you have sex, your making a covernat speaking to the earthly and heavenly relms.Its only Jesus' blood that can break the covernant we made.In the olden days sex was the mark of marriage not a ring nor did they have marriage vows.We say the vows so that we realise the seriousness or our covenant.People take the vows more serious than sex.People generally,say the vows maybe once in their live but sex,people have casually deminishing its value.So what if i realise the seriousness of this covernant and so does my "husband"(to be),why cant i have sex?Sex is ment to be in the right context or people should have sex with the right mindset?Is the right context the right mindset?right context = right mindset?
I hear a "NO".My flesh does not like the sound of that.In Gen when God created Eve.He showed Eve to Adam,God presented Eve to Adam.I guess God shows you who your husband or wife.The priest is an extension of God when he marries you.God, the priest and th wifes father presents the her to her future husband.The husband has seen his wife as "bone of my bone"
As you see below,its speaks of husband and wife not man and woman

1Cor 1:1-3 1 Now concerning the things of which you wrote to me: It is good for a man not to touch a woman. 2 Nevertheless, because of sexual immorality, let each man have his own wife, and let each woman have her own husband. 3 Let the husband render to his wife the affection due her, and likewise also the wife to her husband.