Yes, I believe you have a right to be upset.......In my book cyber is a form of cheating.......I think you should have a real open sit down with him on this subject......
I do know men that love to cyber and never stray from their mate....However, I am not suggesting this is right......
Just the fact that this is upsetting to you should be enough for him to stop doing it......
Talk to him......Try to not let it be an argument.....Let him know that it is something that bothers you.......
Good luck......I hope it works out well for you......