Generally dating a co worker is not a good idea, if $hit hits the fan she can accused you harassment and say by to your job and potential employers.
Second, if you didn't wanna be friends why did you agree to it? She probably unfriended you cause maybe she still likes you and don't wanna see you with other women.
If you keep with the small talk you're behaving like an orbiter and an entertainer when she's bored, if that's not what you want, stop it.
If you wanna date her again, invite her out to drinks and make a move, no need to apologize for being a man and desire her, if she says no, then its a done deal, you move on and date another one.
But remember, you can be fvcking your career over, in today's world if a girl accuses you of $exual harassment, first they fire you and later they ask what happened.
It almost happened to me, good thing they were other witnesses, but never was the same cause women like to talk $hit and lie, I had to change jobs cause she fvcked my reputation.