As long as it isn't threatening or rude or evil in some way.
NO its not ok to date your sister ex boyfriend that nasty to date your sister ex boyfriend i would never date my sister ex boyfriend and i hope she wont date my ex boyfriend
It is never okay to date your friend's ex-boyfriend.
He truly does not love you so leave him.
how do u get ur ex boyfriend to leave you alone???
"I still like you."
NO
Maybe. My daughter married her ex's best friend. They both discovered her ex was a jerk.
It's okay to be in touch with an ex, but if you are currently in a relationship, constant contact, and in some instances, any contact with an ex may not be appropriate. If it is a situation where two exes still really like one another, the current partner is going to feel inadequate, and that could be grounds for a breakup.
either he wants something to remember her by or he still got feeling for her
If this were to happen, it would likely not be your business, so it's okay.
if he thinks it's ok then sure.
"He is your ex boyfriend" is correct.If you were to say "he was your ex boyfriend" it would suggest that he is no longer your ex.