Praise be to Allaah.
It is not
permissible for a fiancé to touch his fiancée, or be alone with her, or kiss
her, because he is a stranger to her (non-mahram) until the marriage
contract is done. It is only permissible for him to look at her when
proposing marriage so that he will marry her knowing about her, and this
could help to make the marriage successful.
this, what you mention about touching the breasts etc is haraam and he has
to repent from that, as well as regretting it, praying for forgiveness and
resolving never to do that again.
Each of them
also has to keep away from things that may lead to temptation and things
that may tempt them to do haraam things, and they should be keen for their
married life not to start with disobedience towards Allaah, may He be
mentioned do not mean that the girl becomes haraam for him (a mahram), even
if we assume that he breastfed from her, because breastfeeding of an adult
does not have any effect, according to the majority of scholars. See also
question no. 2864.
referred to in the question has to do with sucking the breast and drinking
milk, not just kissing or sucking without milk being produced.
To sum up:
all they have to do is repent to Allaah, may He be exalted, and they should
hasten to get married if possible.
treatment for waswaas is to remember Allaah constantly (dhikr) and to offer
prayers regularly on time with the congregation, and to adhere to obedience
to Allaah, may He be exalted. Then one should ignore the waswasah and not
pay any attention to it.