The man made a mistake from onset. What's wrong to tell your partner that you do gamble, at least in the early stage of the relationship, she will consider if she will cope with it or end it. At the same time, I dont think it is wise to end a strong relationship because you find out that your partner is a gambler. Things like that can be fixed, highest she demand for change which will come in due time.
Both of them have made a mistake. One failed to communicate while the other acted impulsively.
they have been together for a long time maybe after some time apart they will realize some things and will get to talk together
i do not think gambling is the worst thing here but the fact that he hid this secret from her maybe if he were just honest they could have talked it out