Like both of them get jealous seeing the other one talking or getting too friendly with a member of the opposite sex for e.g. hanging out with them alone etc. They haven’t confessed any feelings for each other and they are not friends.
When two people get jealous after seeing the other talking or getting too friendly with a member of the opposite sex, it often means that they both feel possessive of each other.
In other words, both of them want to be at the receiving end of attention from the other with no one else getting in the way.
Even though they haven’t confessed any feelings for each other and they are not friends, there is a part of both of them that hopes that through some fortunate circumstance, they will be able to become acquainted.
However, neither one of them is willing to make that first move because they would much rather have the other risk the possibility of rejection.
If they are making each other jealous, they could be experiencing a connection that doesn’t require the both of them to be together, be friends or talk on a regular basis.
There are people who can develop an emotional connection with someone that they don’t know at all based on attraction and the stories that they have allowed themselves to make up in their minds about what that person must be like.
The stronger the attraction, the stronger the stories. This is often where the feeling of possessiveness comes in.
By this point, they have made up this other person’s persona, lifestyle, passions, dreams, history, etc.
In essence, they have created a surrogate version of this real life person in their minds. They become possessive of the persona that they have created.
Once they see this person talking or getting too friendly with a member of the opposite sex in real life, it goes against the fantasy that they have made themselves believe about who this person is and the connection that they both share.
This is often what will cause them to become jealous.