Very often, when breaking up, people will say: "You are not the person I met" or "You are not the one I fell in love with", while it is possible for someone to change, what often happens is that, in Jungian terms, the projection fades & you are faced with the truth.
In the process of animus or anima projection, it is not the other person we appreciate or love, it is part of ourselves that has not been integrated into the conscious mind. This creates the neurotic, immature bond of "falling in love" & disenchantment follows once it fades.
If you have a clear image of what is ideal man & it is very rigid, or if you have a very clear image of ideal woman & try to mold real life women into it - it means that you have not integrated this part of you. You reject it in yourself but you seek it externally.
With this rigid image, you usually struggle to connect maturely with those who are your romantic interest because you cannot relate to them as a person. You can only relate to them as an image that is in your head. It is neurotic & unsustainable in the long term.
What you can do: Meditate on that ideal woman/man you have in your mind. Is he powerful? Troubled artist who needs saving? Is she nurturing mother? A wild Amazon? A seductive vampire? What characteristics does he/she have that you want to develop in yourself?
If your male idea is powerful King, it does not mean you will get inside the government. It is an internal process. Maybe you want to rule over your impulsivity, your neuroticism? Maybe as a man you want to enjoy fashion & perfumes hence you have Venus as ideal?
When we integrate the animus/anima we “fertilise” our own psyches & we become complete. Individuated. Then we can truly appreciate & relate to others. Until then, it will probably be endless repetition of certain patterns & often very painful/unfulfilling/forced.