Will it be possible to make the MC the only one who has a romantic and sexual relationship with ALL the LIs (i.e., the LIs don't have open relationships where they sleep with other people, whether male or female, and any LI with a previous relationship ends it the moment she starts being with the MC)?

I want to make this possible in the future, and when complete, change the way the game is currently played, which requires you to complete all the missions to move forward. 

In 0.4, I want to make the main mission and the relationship with each girl separate.

 With this, it will be possible to complete only the missions with the girls you choose, without having to go through other missions. 

Pre-established relationships may or may not continue after a certain part of the route, depending on how the game develops, but I want to keep the possibility of choice if possible.

I actually want to avoid establishing a relationship with any LI who can only have an open relationship with the MC (i.e., if she can sleep with other guys or girls I want to avoid any relationship with her).  In fact, if the relationship starts out open, I don't care how it develops because I don't want the MC to start it. 

Also, I only like having sex with LIs who have a previous relationship if they have left that relationship and started a romantic relationship with the MC (a exclusive relationship, she doesn't have sex with anyone else besides the MC). In fact, the LI and her partner must cut off before the MC and the LI begin their relationship and have sex.

Is this going to be possible?