Continuing to be friends with my ex bf

I want to make this as short and simple as possible for you guys so pls bear with me.

My ex bf and I were on and off for a few years during and after high school (during college too). Things weren’t working out and he kept disappointing me with his actions and his lack of effort in the relationship. I ended up breaking up with him and he just told me he didn’t have the time anymore for a relationship or gf and we basically ended it there and on mutual/good terms.

We remain really close friends and support each other and talk frequently about life and our struggles etc. We also share the same group of friends that he actually introduced me to and I’ve been getting along with the girls in this group. I kinda feel weird about it since he’s my ex and I’m hanging out with ppl he knows, but at the same time I get along with them and I honestly could use these girls as new friends.

I obviously care about him still and he’s told me he cares about me too and I’m not expecting anything to change or for us to get back together. My sister though thinks I should just stop talking to him altogether, but it’s hard for me to do so. I’m definitely emotionally attached. However, I don’t let this affect my dating life and I’ve talked to other guys and flirt with some at the gym.

Idk what to do… completely cut him off for no reason or just leave things how they are? I hate the feeling of people around me judging me for talking to him still.