Is chatting with girls online considered unlawful (haram), and does it invalidate the fast in Ramadan if a very small amount of semen is discharged, and what is incumbent upon me then; is it making up the days or expiation?

A man's conversation with women, even if it is forbidden by Islamic law, does not invalidate the fast, although it may diminish its reward. However, if the conversation is accompanied by the emission of something from the penis: if it is madhy (pre-seminal fluid), it does not invalidate the fast according to the most preponderant opinion; but if it is maniy (semen), there is a difference of opinion among scholars regarding its invalidation of the fast, and it is more prudent to make up that day.