If your man suddenly stops calling you could he be cheating?

I'm not sure it is a signal of cheating, but I would be quite curious as to who is calling that he is not comfortable talking to while you are around.

It could be something that he thinks you will think is silly so he doesn't talk to them around you, but of course there is always the chance it is something more serious.

See if you can find out who it is that is calling that he is ignoring.