Entity Reference Issues - Ending Records?

Have been using drupal for a while but still a bit of a newbie. This is what I am trying to do:

I am creating an "asset tracker" to track assets in our district and to also assign the asset to students/faculty. I have content types of assets, students, faculty and repairs. In the system I can add new asset, add new student, add new faculty etc. I am then using entity reference to tie these together. This is all working. When I add an asset to a person or a person to an asset it adds it on both ends. Yay! So that works. The question I have, I also need to be able to "end" this "assignment" if a faculty or student leaves and then re-assign this device to someone else. I have tried this two ways, one as listed above and the other I moved the asset tracker to a sandbox and created a content type of "assignment" and was tying the records together with an assignment ID. The problem I have either way is when I "end date" the assignment the end date does go in the record but then the record still has the "assignment ID" or on my live version it will still have the studentID on the asset and the asset ID on the student/faculty. So due to this the device will not go into unassigned devices and you can't see that the student does not have a device. I do not want to have to remove the assignment or asset from the student and put a "note" that the item was assigned at one point. I want to have data integrity and this will lead to mistakes and records being incomplete.
Any advice? Am I missing something or is this just not do-able with entity reference?

Thank you for any advice!