They Start Getting Really Busy With Work
Imagine that your partner has to spend long hours at work because they have to work on the latest project. That might be the case with some jobs, but if they didn’t stay at work before and now they started to do so, you have a good reason to believe that something strange is going on in their lives that you are not aware of.
Only time will tell if they had to work overtime or not. What is funny about this is that this is a classic excuse. They don’t know how to make a decent alibi so they just went with the most obvious one – work. Try asking them why they stay up so late at work. If they become defensive it means they might be cheating.