You can’t be sure your boyfriend is not cheating on you. The best indicator is his behaviors, and they are what is causing you doubt.
There are many ways you can spy on him, even from afar, and there are many ways he can hide things from you. If you snoop, you are likely to get into a frustrating cat and mouse game with him. Your anxiety will likely increase, and you will waste a lot of time.
Don’t assume your boyfriend is cheating on you. You can discuss your concerns with him, such as it worries you that you no longer speak daily. See how he responds and whether his behavior changes. In time you will likely know why your boyfriend may be distancing himself from you.
All the best,