If there was a true emotional connection I wouldn’t be comfortable with that. I would be too concerned that those emotions are still lingering somewhere, and it’ll be just a matter of time before they come out. If he was really her friend he would respect her new relationship and step to the side. Not to say they shouldn’t ever communicate, but regular and continuous contact is a no-no.
I would say it depends on the length of their relationship. If they were involved years ago, and have been platonic friends since, then I think I’d be asking a bit much for her to give up such a friendship. Now if this is her last boyfriend or a guy she had sex with in the past year, my question would be “why?” What is his purpose? Friends you’ve met in the past year are a dime a dozen, and any emotional role he was filling for you is supposed to be my job now. What is the purpose of maintaining a relationship with this guy? Granted, there are exceptions to this as well, but I’d have to hear a reasonable answer to those questions.