What is the ruling on someone who fondled his wife during the daytime in Ramadan, then left her when he felt semen about to be released, but then semen was released about a minute later?

It is not permissible to fondle one's wife during the daytime in Ramadan if it leads to the emission of semen. Your fast has been invalidated by the emission of semen, and you are required to abstain [from eating and drinking for the rest of the day] and make up the fast. There is no expiation required of you according to the majority of scholars, while the Malikis hold that expiation is obligatory in addition to making up the fast.