Praise be to Allaah.
If the scars from
the burns are large and disfiguring in a way that could be off-putting to
the husband, it is essential to tell him before doing the marriage contract,
because withholding that information is regarded as deceit. The basic
principle is that any defect that could be off-putting to the husband and
prevent fulfilment of the aims of marriage, namely compassion and love, must
be disclosed and it is not permissible to conceal it.
This has been
discussed previously in the answer to question no.
But if the scars
are not very visible or they are unlikely to cause the husband to be put
off, then you do not have to tell your fiancé about it, because that is not
regarded as one of the defects that would affect the marriage.
In the event that
it is obligatory to tell the husband about it, that could be done through
your father or brother, so that you can avoid talking to your fiancé
unnecessarily, because he is still a non-mahram to you like any other non-mahram.
We ask Allah to
help and guide us and you.
And Allah knows