SureAI

how can i return to halfmoon island to get the soul? atm can't open three doors at the living temple even if i put smth heavy on these buttons

Welcome to the forum

Unfortunately not. You can only visit halfmoon isle once in the game as part of the quest.
You would have to load a previous savegame

i think that is not very fair not to have an opportunity to collect all souls while failed once. is there any opportunity to get this soul in any other way?

There are two places in the game that you can only visit once. Halfmoon Isle and

[+] spoiler

Old Dothûlgrad

It should not be too easy and increase the replay value.

well. the difference between my saves are about 15 levels. that is huge in terms of done content

Read your pm
And save more often

Don't know what Kermit's pm might have said, but if you are desperate, you can add that soul using the console;

[+] spoiler

player.additem 0101e9d6 1

It is unfortunate that sureAI chose to put some collectibles in locations that cannot be revisited. In the case of souls, for example, a player might not decide to collect them (or even look for them) at the very start of the game. One might decide to try out that phasmalist stuff after being well into the game, quite possibly past Old Dothûlgrad. Contrary to what Kermit seems to suggest, doing this does not increase replay value; someone who has already invested 50 or 100 hours might not want to replay just because one soul was missed, or just to get an "achievement" ticked off. Also, the very many long, drawn-out scripted dialogs that cannot be fast-clicked through are a deterrent to replay, as being forced to listen to so many dialogs adds hours to a replay, which is unnecessary if one already knows what is being said.