As much as it can be to watch someone hurting you can’t do anything to make them happy. You can offer support or assistance in getting over whatever it is they are going through.
But the final responsibility for the last effort depends on the person that it matters to the most — the hurt person.
The problem with this is that it can lead to all sorts of defective behavior. The unhappy person can use the leverage, perceived or not, to control those around them who are trying to help them. This can range from pure passive aggressive bullshit to just being unaware of the problems they themselves are causing to those who are only trying to help.
Looking at someone hurting is hard.
Trying to help them is a natural response.
Helping to the point that the problem is worse than the cure just damages everything.
Trying to help someone who doesn’t want to be, or can’t be happy will simply cause pain.