Most Helpful Guy
Because he's between women and he wants to use you as a backup plan till he finds someone else
Most Helpful Girl
Well occasionally people have regrets or something else was going on at the time they couldn't talk about. But unless they explain properly it can be pretty freakish. Because you don't know if they want you for the right or wrong reasons. Especially depending on whatever caused the breakup in the first place. Maybe they think you're both older and mature it can work out now. But if your not feeling it make sure they know you have moved on. That maybe you could be friends unless how things left off (or their present behavior is too weird) then you might state you aren't into friendship either.