It is so hard to trust when they work together.....I know from experience. My situation they worked the same shift and he had the latitude to visit any time he wanted. He was in IT repair.
I think only you can answer your question. I would ask you, do you think the same shift will hurt or harm your chances of R? The same question as moving shifts? One thing you might consider as a third option, is to try the day shift, if it does not work, then change shifts.
I would imagine it would be hard to get back to days, at least it is in many jobs. So this could be a long term challenge for you.
The reality is as long as they work at the same company contact is possible. You will be challenged with accepting it. However, if he continues to tell you at every contact and you believe he is being truthful, hang on to that.
I know how hard it is....hugs to you.