I dated two married men seriously. One was separated when met him. The other one didn't tell me he was married until we had been dating for several weeks. I was too much in love and too stupid to stop seeing him right away. Both gave me presents, wined and dined me, but neither, of course, had the slightest potential as a husband.
Married men have lots of lines.
Don't believe any of it. Like my second married man, some will even lie and claim they're single. There are lots of signals that a man is unavailable. He doesn't give you his home phone number. He doesn't see you on weekends or holidays.