I am not sure "getting over it" would be the term I'd use.
But moving forward with your life as a couple and becoming stronger together is possible, with the right amount of effort.
4 months isn't as long as it might sound. You are still healing that open gash in your soul. It will take a while for it to heal up.
"Mind Movies" are normal, I have OCD and I often obsess over them, not just about his affairs either, just general life stuff. What my IC has taught me to do is force the Mind Movies away, focus on something else. Accept that they are there, but to not allow them to take control and it does help me a lot.
I usually sing in my head as a distraction. I like to recite the alphabet lol because it's something I can do without REALLY thinking.