I have always found Martin Platt to be an unsympathetic, arrrogant character. He treated Gail really badly, he pressurised her into going ahead with her pregnancy with David. He also pressurised her into buying the new house on Coronation Street. He disbelieved some of the things, Gail was concerned about earlier in their relationship.
It's funny how these issues were never addressed, or maybe they were, I stopped watching Corrie in the 2000's for a number of years.
You can understand how David became the person he is, with a role model like Martin!