Peter and Sadie Keogh, from Enniskillen, are going to Stormont on Tuesday to call for greater regulation of the industry.
Lewis was 34 when he died by suicide in 2013. He was about £50,000 in debt.
"All he could see was a dark hole - he didn't know where to get help," his father told BBC News NI.
Had there been stricter gambling regulations, Mr Keogh says "you would have hoped there was a chance that he could have seen a way out of it".
They are calling for clearer health warnings about the dangers of gambling, a ban on aggressive marketing and specialist treatment services.
They also want an independent regulator such as Great Britain's Gambling Commission.
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