Dartford last week put in a seven-day notice of approach for the player and have spoken to Collier since the game at Weston-super-Mare on Saturday.
Hampton manager Alan Dowson told his club`s official Pitchero website: “I’m devastated.
"He’s probably one of the top three players I’ve signed, but I can appreciate why he’s making this move.
“He lives a lot closer to Dartford than he does to us. He and his partner are about to have a child and he understandably has their interests at heart. Dartford are a well-funded club and were able to make him a very good offer.
“Nathan was nearly in tears when we spoke on the phone. He loves our club and appreciates the help and support he gets from everyone. He also gets on well with the supporters.
“However, it all makes sense for him and, while I don’t want to see him go, he leaves on the best of terms with me.”
Collier has been with Dartford before, as well as with Eastbourne Borough.
He was Hampton`s `Mr Versatile` in his two years at the Beveree, having played right across the back four this season.
He’s also an accomplished midfielder and was even pencilled in to lead the line in one game.
Dowson is confident he will be able to sign a defender to cover the loss.
(Photo: Leigh Page)