wWhy ishas the divorce number become so high this days?

Capitalization for all sentences. Adding in has shows that the number increased in the past, and now we can talk about it. I added so to make it flow better.

fFirst, let's talk about marriage before we explain to why the divorce number is increasing nowadays.

You don't need "to".

mMarriage connects two strangers who don't know each other before or have been in contact for some time and also lovers who have been together for a long time and decided to announce they are officially husband and wife.

tThen the question arises here: why are they separating if they were in love and decided to live together?

bBecause in my opinion after they start spending a lot of time together they begin to know a lot of weak and bad habits of their mate andspouse. They will start to question whether they know their partner's true identity or they werewere they blinded by their love and decidedmade a wrong decision, t. The same is true for the other partner.

"Mate" is technically correct, but gives the impression of something more animalistic (like cavemen or animals). It's also a common British slang for a friend (less common in the US but recognized), like "He's my mate." Spouse or partner sound better.

The sentence starts to run on, so I broke it into three sentences. I framed the last part of the second sentence as a question, similar to the first part. Both are grammatically correct though. "Made a wrong decision" sounds more natural than decided.

aAnother cause of divorce is poverty, when the husband doesn't fulfill house demands, the wife will begin to lower her love towards him intentionally or unintentionally.

Or the wife's salary doesn't fulfill the husband's needs either. :)

aAfter that, she will not treat him as before, and then the husband lowers his confidence and starts thinking of negative things, e. Even if she says something positive, he will interpret it in negative ways, and then, boom here, then begins the argument and fight.

This needs to be two sentences or else it's a run on. Argument and fight have the same meaning, so I took out the last part. Instead of "here", I said "then". "Here would be natural when speaking, but less so when writing.

wWhy is divorce number becomthe rate of divorce higher thisese days?

Corrected for clarity and tense

fFirst, let's talk about marriage before we explain to why the rate of divorce number is increasing nowadays.

mMarriage connects two strangers who doidn't know each other before or, people who have been in contact for some time and also, or lovers who have been together for a long time and decided to announce they are officially become husband and wife.

I'm very surprised you're saying strangers marry each other! I think that's quite unusual in the anglophone world and could maybe use a bit of explanation when writing in English. Also, "announce" says to me that they were married previous to the announcement, so I think "become" works better here.

tThen the question arises here: why are they separating if they were in love and decided to live together?

Correcting mostly for style. "Here" doesn't sound great, but is definitely correct.

because iIn my opinion, after they start spending a lot of time together, they begin to knowdiscover a lot of weak and bad habits of their matetheir spouse's bad habits and will start to question whether they know their partner's true identity or whether they were blinded by their love and decidedmade the wrong decision, t. The same is true for the other partner.

Usually, we don't start sentences with "because." "Mate" is also used more often for animals than humans.

aAnother cause of divorce is poverty, w. When the husband doesn't fulfill household demands, the wife will begin to lower her love towards himve him less, intentionally or unintentionally.

I'm curious what household demands (or tasks?) are! I don't think that's clear.

aAfter that, she will not treat him as before, and thenshe did before. As a result, the husband lowerses his confidence and starts thinking of negative things, even ifly. Even when she says something positive, he willmay interpret it in negative ways, and then boom here begins the argument andly and initiate a fight.

Your sentences also tend to be quite long! Sometimes, they are run-ons (as in the above case). Sometimes, they just need to be a bit shorter stylistically and for ease of understanding.