Is it wrong to date him?

There is a guy pursuing me who was in a relationship with and has a child with a girl I also used to friends with. The girl and I were friends in high school and she became my roommate for 6 months, but I had to put her out for not keeping up with her portion of the bills and keeping my house like a pig sty and bringing multiple men in and out that she met on myspace. Our friendship ended very bitterly over 2 years ago because of those things. The guy has been pursuing me for 8 months already, I still wont even go on a date with him. Their child together is 6 years old and lives with him. They haven't been together for over 3 years. I like him, but it is ok for me to go on a date with him, do i still have to respect the dont date a friends ex "rule" even though she and I aren't friends anymore??