There is an argument if having a mistress is okay and most rishonim allow this. but even the Rambam who does not hold it is an איסור עשה [prohibition derived from a positive command]. That is how the Beit Shmuel in Even Haezer explains the Rambam. For the Rambam does hold that a girl who is willing to have sex with anyone for money--i..e. a prostitute is forbidden, but  that is not the same thing as when one has a mistress or girlfriend who is only for him alone. But to most rishonim this is permitted outright.

The Gra makes note of Caleb ben yefuna in chronicles I ch 2 verses 43-50 who had a few wives and a few mistresses. And he was not a king. So the Rambam who says that a mistress was permitted only to kings is incorrect. 

As the issue of the monthly period, she should dip in the sea or a river

 The white race is committing suicide. It is not enough that everyone else is trying to wipe them out but at least half of them want to destroy their progeny and traditions. This is sad because if the USA goes under, where could be any bastion of freedom? Maybe Israel?  

 I was looking at vol I chap. 19 in the book of Rav Nahman and noticed a few things. One is the approach that he takes towards sex. The general desire for sex he calls ''desire for adultery''. He is not thinking at all the sex in marriage all of a sudden becomes holy. It might be permitted but still has that aspect of ''desire for adultery''.  But this is not new to me. You can see in the Mesilat Yesharim that sex can be holy once one has gone through all those preliminary steps enumerated in the braita of R .Oinchas ben Yair. Mainly however I would say that a lot depends on intension.

In fact it makes sense to learn the sidur of Rav Yaakov Emden for newly married couples which goes through this subject in detail.

besides that i have no idea why people think marriage makes anything better or holy. i have repeated plenty of times the story about the friend of Joshua [who conquered  the land of Canaan] Caleb ben yefuna in Chronicles chap 2 verses from around 43 to about 50.  it is hard to tell how many wives and how many girl friends he had but clearly they were quite a bunch. and hewas not some low life. וימלא אחרי שם ''he went totally after God'', [see rambam at the start of laws of marriage and the raavad and ramban there. ]

The approach to Kant called the Friesian School does not engage with the major interpretations of Kant. It sort of stands alone  ''Take it or leave it.'' as you might hear when you go to buy at the supermarket.

I think this isolates this school  from academia, and also makes it hard to place in the Kantian Spectrum.  

I mean  to say that the major interpreters of Kant are Cohen [Marburg school], Allison, Strawson, Sellers. [The later Cohen diverged from Kant.] And besides them there are the many approaches influenced by Kant--like the later Cohen. Where does immediate nonintuitive knowledge [of the Friesian school] fit or not fit with all this?  In what areas do they agree and in what areas disagree and why? 

 In the approach of the Gra there is an emphasis on the "Seven Wisdoms". Rav Baruch of Shkolev was a disciple of the Gra who wrote a small translation of Euclid and in his introduction quotes the Gra: ''Anyone who lacks any knowledge of the Seven Wisdoms will lack in understanding of Torah a hundred fold.''

Bur what can this mean? The Seven Wisdoms is a well known concept of the Middle Ages. [grammar, logic, rhetoric, arithmetic, geometry, astronomy, music ]The emphasis on learning them is found in some rishonim  besides the Gra, but certainly not all.

[My approach to this is to emphasize Mathematics, and Physics but Astronomy I feel not ready for until I have a good grasp on General Relativity, QFT and String Theory. For the ultimate test of Strings will have to be in the distribution of the stars and galaxies.

[Even if Physics is hard, I figure that with the approach mentioned in the Gemara about review 400 times, it must get clearer after a few hundred times.[That is the story about the amora who used to review each lesson with his disciple 400 times. Then once his student was not concentrating so that amora reviewed the lesson another 400 times.]]

why not to believe everything doctors say

 Radithor-- or why not to believe everything doctors say--especially about new treatments, This was wifely prescribed by doctors. This was given to a well known athlete who had a minor  discomfort.  After taking it he felt great.  It had all the properties that were advertised. It relieved pain, made him feel great, and gave a tremendous boot of energy  So he kept on taking it until after some time his jaw fell out. It turns out the main ingredient of Radithor is Radium. [radium is radioactive.]

[This is the true story about about Eben Byers]

 I have always strived for monotheism even though I admit that I miss the mark by a wide margin.

See Deuteronomy 13 and the general chapters in that area. There is a lot of emphasis on not serving any other gods besides God the one First Cause with no form nor substance and is not a composite. Just to give you a few examples--Anyone you see that has served other gods, you should stone to death. A city that idolatry is wide spread,... you should burn to the ground and kill all its inhabitants. Any prophet that even gives true of his prophecy and works miracles you should kill. [not by stoning.]  

So once the Gra made it clear with his signature on the letter of excommunication what is included in the prohibition of idolatry, it should be clear. that signature is sadly ignored by all, but I still feel that at least I ought to pay attention to it. 

But why is the Gra ignored-because of the mixture of Torah with money. People make their livings off of Torah and so can not see straight.