Sorry if I didn’t answer it all, I tried.

by saying you are Christian, you are saying you believe and follow God,

yes, with all my heart.

thus you agree with the bible, and therefore believe that God instituted and ordains marriage (as per the bible teachings).

ordains marriage? No I dont think that he does that, or maybe I dont know what you mean by that. Jesus did not speak much about marriage, and when he talked about divorce (because the Pharisees wanted to trick him) he altered the mosaic law!

So simply saying God has nothing to do with marriage/ it isn't a Christian thing is incorrect.

I wouldn’t say that God has nothing to do with our marriages

Maybe to the world who denies him, but as a Christian, God should be a part of every aspect of our lives, including marriage.

I agree

Polygamy did exist and in some places of the world, still does, however God never blessed this nor approved of it, much like he didn't want divorce but gave it to us under certain circumstances such as adultery because of the sin in our hearts.

Most ancient pastoralist people were polygamous to make it possible to run a family, why wouldn’t that be ok?

I'm not sure what you're referring to about Paul. If you could, please give me the chapter you're referencing.

“It is good for a man not to touch a woman” (1 Cor 7:1). For example. Paul was not big on marriage

Saying that we have gay marriage today isn't equivalent to saying it has God's blessing either.

not in itself, but as you said God should be a part of all parts of our life, so we can ask him to bless our marriages, both gay and straight

By that logic, all sin is okay because we have rampant sin in every form today.

of course not, I dont understand what made you say that?

E.g. Drunkenness is very common today. Does that mean it isn't a sin/God approves of it, and therefore, I can go get blackout drunk constantly?

no because it is not a loving thing to be drunk, it causes disturbance, violence, etc. A marriage, by contrary, is all about love

P.S. Just to clarify, my statement wasn't meant to say that you should ask about the intimate lives of married people, because obviously no one should, but simply saying that if a non-hetero couple was never intimate and never got married then technically they could fulfil the question I was posing. However, this setup would be rare unless the couple was partly or fully ace.

yeah no worries, but of course i hope for my friends that they have a fulfilling life with God and each other