I’m doubting if the breakup is caused by mistrust alone other than the fact she don’t like the idea of gambling and seeing her spouse engaging in such activity makes it complicated, although the man is at fault here because sometimes sharing secrets with a close person might not get them upset rather hiding such from them makes it bad. In my opinion her choice of leaving sounds over reacting basically gambling is not bad compared to all kind of criminal act, at this point self discipline is needed when engaging in gambling activity well relationship built on lies might one day end on the wrong side.