This might be "Planets of Adventure" by Murray Leinster - I found it as an ebook, but it is also available as a softcover. The second ~half of the book, is called "the Planet Explorer" and has a set of short stories, starting with "Solar Constant", which centers around a character named Bordman, who is an engineer and Colonial Survey Officer, who travels to different planets and tries to make sure everything is going well, and who ends up fixing problems as he finds them.
The first part is about a colony on a dangerous planet covered in forest. The second part in this story is where the main protagonist goes to a new planet with the colony, and this new planet is a desert.
The first story has him dealing with a planet which is becoming colder and freezing too much because of sunspots, and the second story is about a desert planet which had trouble from sandstorms. Other planets include different locations, including an upside-down swamp, and a forested world (actually third in the series).
On the first planet the protagonist arrives in a craft, and after a few events dealing with the hostile jungle that surrounds the clearing the colony made, he becomes a sort of leader helping the people to survive.
In the first story, he saves the colony and does become sort of a leader there - offering things to try and fix the problem and improving solutions until something works. It is not exactly a forest world, but there is a forest world in the third story, and several other stories in the collection have forest or jungle settings (including the first half of the book which has a very dangerous jungle planet) which you might be mixing with this story.
I feel like I remember him meeting his lover on the first planet and she stays his lover through the second planet as well.
He gets married, at the end of the first story - and there's a mention of subsequent adventures which call him away from his family, but who he gets back to between calls.
