That's a lot crap.
If he is spending the night with another woman that was enough proof that he had sex relation with her and you could get df and would be enough proof of adultery for a mate.
He does not have to have sex with her but just play around with her sexually and it is considered gross sexual misconduct.
You better talk to your mother about it and to the elders. The stuff below is from the elders book
Loose conduct is a shocking, flagrant disregard for Jehovah's
moral standards. (Gal. 5:19; w83 3/15 p. 31; w73 9/15 pp. 574-6)
It may include the willful practice of heavy petting or the fondling of breasts.
The nature, circumstances, and actual extent of what
has occurred may indicate loose conduct, which would require judicial action.
Such practices can easily lead to por.nei´a.
" Por.nei´a"
involves immoral use of the genitals of at least
one human ( whether in a natural or a perverted way ), and
there must have been another party to the immorality‹a
human of either sex or a beast; willing participation incurs
guilt and requires judicial action. It is not a casual touch-
ing of the sex organs between persons but involves the
manipulation of the genitals. (
w83 6/1 pp. 23-6;
w83 3/15 pp. 30-1)
Strong circumstantial evidence, such as pregnancy or evidence
(testified to by at least two witnesses) that the
accused stayed all night in the same house with a person of
the opposite sex (or in the same house with a known
homosexual ) under improper circumstances, is acceptable.
It includes oral and anal sex or mutual masturbation
between persons not married to each other, homosexuality, lesbianism,
fornication, adultery, incest, and bestiality. (Lev. 20:10, 13, 15, 16;
