I'm not judging. But, there are "no" reasons why anyone can not leave someone. Children get accustomed to change, finances can change by making them change, family/friends help out when needed.
What I am saying is no one should live in a loveless marriage/relationship if they have tried and can not work together to make it work. But, no partner deserves to be in a lie of a relationship either, including affairs.
Going through this for another 3 months, never being able to hold each other or find out if you both are actually suited or if it is just lust of things missing in both of your lives, is far harder than to walk away and establish if there is something worthwhile between the two of you.
Asking how to assist in you sneaking around behind a partners back, sorry I can't help you with that answer but I do hope, you consider both of you, the reality of all of this and discuss as Adults how to end things with your significant other halves nicely..
You do say your other half is over protective, don't you mean possessive? I could stay with someone a girlfriend or family over night.