Have to agree with the previous answers.
His 'friendly advice' - is there another kind? - is a response to your attitude concerning his marital status, which is entirely your choice and your right.
Perhaps he feels a little guilt, and as such he feels peeved that you have decided to opt out of an on-line reletaionship with him, so he felt the need to have a pop at your insecurity.
Ignore him. This man does not know you, and is obviously not qualified to make such suggesttions - 'friendly' or otherwise.
You can pick and choose how you live your life on a dating site, he, by defintion, cannot.