Sotah and Terumah

 

וַיְדַבֵּ֥ר יְהוָֹ֖ה אֶל־משֶׁ֥ה לֵּאמֹֽר:

דַּבֵּר֙ אֶל־בְּנֵ֣י יִשְׂרָאֵ֔ל וְאָֽמַרְתָּ֖ אֲלֵהֶ֑ם אִ֥ישׁ אִישׁ֙ כִּֽי־תִשְׂטֶ֣ה אִשְׁתּ֔וֹ וּמָֽעֲלָ֥ה ב֖וֹ מָֽעַל:

איש איש כי תשטה אשתו: מה כתיב למעלה מן הענין ואיש את קדשיו לו יהיו, אם אתה מעכב מתנות הכהן, חייך שתצטרך לבא אצלו להביא לו את הסוטה

This Rash"i begs the question; What does the Aveira of not giving the Kohen his Matanos have to do with a person's wife becoming a Sotah? 

Upon a little contemplation, I realized that there is direct causation here. 

In general, there is an interesting dynamic in a traditional relationship between a man and wife. The man, generally speaking, is more giving and offers  his house, car etc. to others more freely than his wife. Chaza'l in Bava Metziah 87A say:

כתיב (בראשית יח, ו) קמח וכתיב סלת א"ר יצחק מכאן שהאשה צרה עיניה באורחים יותר מן האיש

This, I don't believe, is necessarily a negative trait. There is a ying/yang where men don't always measure the ramifications of offering their house to 12 guest for four weeks while the woman, being more realistic (sometimes) sees it as the impossibility that it is being that all the kids will be home or such. A man might pledge a large sum of money to charity and his wife will remind him that they need that money to fix a leak. In the Sefiros, the right side which starts with Chesed (giving) is known as the male dominated side. The left side which starts with Gevurah (withholding) is known as the side of Nukva-Female. At the end of the day there needs to be a healthy balance between the two.  However, there are many situations where the ying/yang is out of balance. Many times a woman will not want here husband to give anything away to charity and would want to keep it all for herself and her family. Those situations a husband needs to assert himself and allow his wife to understand that "NO" I am the man of the house, I earned this money and I will do with it what I see fit. When the husband doesn't assert himself, he might think that he is doing his wife or himself a favor by listening to his wife. He might think that he is doing what is best for Shalom Bayis. However, he is not! By allowing his wife to control his giving, he is allowing the balance to be destroyed. The wife, whether consciously or subconsciously, wants the man to ultimately make the final decision albeit with her input. If he follows his wife blindly he loses her respect. She won't respect him as a man anymore. 

When it comes to giving the Cohen/Levi Terumah, Maaser, Matnos Kehuna, the same can be said. In a normal relationship the wife might tell her husband to withhold somewhat.  The man's job is to do what he has to do and say no. The husband will not be helping his Shalom Bayis by giving in to his wife. If he does give in to his wife and listen to her and not give the Matnos Kehuna that he is obligated to give his wife will lose her respect for him. The Torah teaches us that the next logical step is that the wife will feel unfulfilled in the marriage and look elsewhere for fulfillment. That is what the Pasuk teaches us   

אם אתה מעכב מתנות הכהן, חייך שתצטרך לבא אצלו להביא לו את הסוטה  

Another potential explanation:

There is an interesting aspect to Matnos Kehuna and that is that although it is considered charity there is also an element of Kedusha to this charity. Not only is it considered giving charity to the Kohen but the Matana becomes Kodesh. The giver is actually being Makdish the Matanah. There is an element of Hakdasha which means that the giver is also giving to God. It is like a hybrid Mitzvah of Bein Adam Lachaveiro and Bein Adam Lamakom. He is Makdish it to God by giving it to the Kohen. One who denies the Kohen his Matnos Kehuna is essentially sinning against the Kohen and against God. 

The only other Aveira that can be considered a sin that is both Bein Adam Lachavero and Bein Adam Lamakom is the Issur of Eishes Ish. When a man gets married he is "Mekadesh" his wife. He creates an exclusive bond. That bond has an element of "Kinyan" which is like any other Kinyan. Now the item is his and anybody that steals, or uses it without his consent would be considered a "Ganav". However in this case of marriage the owner has no right to even consent to allow her to be used by another. The reason is that the woman is "Mekudash". She is his exclusively through a Godly covenant. One who steals her is both sinning against the owner/husband but is also violating an issur Erva which is a sin against God.

This explains why one who doesn't share his Matnos Kehuna with the rightful owner, the Kohen gets punished in this manner. His wife becomes a Sotah. The Sotah represents the same kind of violation that he has transgressed. This is the ultimate Mida Kineged Mida. He violated an Issur Hekdesh by stealing somebody else's item that was hekdesh so his item that is hekdesh too gets violated.