What happens if you still liked your ex boyfriend and he liked you back ? How do you ask him back out?

I like my ex boyfriend still and he likes me back ! He always says hi to me and i say hi back ! I am going out with his brother but my ex is just a sweetheart way deep down ! How should i act towards him and how should i ask him back out ? Please help me and answer my question because i really need a lot of advice ! A lot of people who are viewing my question please answer it !