Praise be to Allaah.
Firstly:
Relationships between the sexes other than in marriage are
among the things that are forbidden in Islamic sharee‘ah. That is because of
the evils that result from these haraam relationships, as is obvious to any
wise person.
We have discussed previously on this website the ruling on
relationships between the sexes and stated that they are haraam, as in the
answers to questions no. 47405
and 59907. In the section on
relationships between the sexes on this website you will find many answers
on this topic.
Secondly:
With regard to what you asked about, the money that you took
from this woman, it may be understood that it was a loan or it may be
understood that it was a gift. If it was a loan, then it is something that
she is entitled to, but so long as she has forfeited her right to it, there
is no blame on you for that.
If it was a gift, then it seems that it was a gift in return
for your continuing the haraam relationship with her, so it is like payment
for haraam work, so you have to give it in charity.
What you should do is give this money in charity, so as to
discharge any obligation.
Our advice to you is to cut off all ties with this girl and
not contact her again.
We ask Allah, may He be exalted, to accept your repentance.
And Allah knows best.