I am so sorry you are in that situation. It must be very painful.

I think (and could be wrong) that the brain has a mind of its own, so to speak.

I read somewhere that there are layers to the brain sometime called the insect brain, the reptile brain, the mammal brain and so on.

Jealousy has a biological purpose in males and females of various species related to the passing on and protecting of one's DNA (I have read).

Sometimes behaviors coming from the deeper levels of the brain do not seem to jive with common sense or our moral or cultural values. So [it is sometimes said] we suffer inner conflict.

In mammals, I have read, males don't want to expend energy on protecting offspring that are not their own. They don't want to advance the DNA of other males of the species.

So males in some animal species while being promiscuous to spread their DNA far and wide are territorial with regard to their mates and expect their mates to be monogamous.

Since caring for young can be difficult and precarious to female animals, females can want to have males around in case the fathers that sire their offspring are lost due to fights, starvation and so on.

A lioness might be friendly with many male lions for this reason. And a male lion is watchful of the female with which he has mated.

When I have felt some of the emotions, moods and inner conflicts you describe, I have often tried to remember that I am dealing with my animal brain which doesn't care about human moral or cultural values. This has helped me.

Of course the whole theory I have set out above (and probably poorly) may be mostly or totally false. Just because a hypothesis or theory seems to make sense of data, doesn't always guarantee that it is true.

Wish I had something more helpful to offer but sadly I am at a loss. I hope others here will have wiser and better words for you than my poor words! And sorry again you are conflicted! My heart goes out to you.