Hamilton will race for Mercedes this season after signing a three year contract in September last year.
Team principal Martin Whitmarsh has insisted that McLaren attempted to retain Hamilton, but Dennis disagrees.
"'I think it's wrong to portray that Lewis left this team," Dennis told CBI magazine.
"At the end of the day, you end up with a situation where you're going to separate if the circumstances aren't right. Life isn't about one person deciding anything. It's never that way. It's about circumstances."
McLaren is thought to have offered Hamilton a financial deal similar to the one he accepted from Mercedes, although Dennis insists he is not bitter about the departure of his protege.
"Everybody says, "Am I bitterly this or bitterly that?" What? I'm a realist. Did we have the ability to create a situation where we could have stayed together? Categorically, yes. Would that have been the right thing to do? We didn't think so."
Dennis added that he remains professional although understandably doesn't wish his departing driver huge success.
"Whatever people choose to do at the end of a contractual period, the professional thing to do is to be supportive of the other side. We don't wish him every success at Mercedes - that's understandable, as he's obviously going to be a competitor - but we don't wish him anything negative."
Sergio Perez replaces Hamilton at McLaren.