Asking for a friend.. How will you tell your 7/o son that you are now dating another guy? He's aware that his mom and dad are no longer in good terms and are not married.

I agree with Beatriz. It's best to hold off the meeting part until everything between the dad and your friend has subsided. After that, I suggest to take it slow for the child. Why not introduce the new guy as a friend at first? Then maybe that's where your friend can start working on. Personally, I think she should just keep it that way until the kid is big enough to understand things even better, so as there wouldn't be any confusion. At 7 y/o, it's hard to grasp things like intimate relationships. Again, that's just my two cents :)