How to not need reassurance

That is my biggest problem In my relationship, I always need REASSURANCE. I hate it, like I told my ex, I still care, I still love him, and I miss him, and he said it on his own back to me repeatedly. I told him I wanted to start over. But it's like... was he saying that to be nice? But I know he's not the type of person, because he says what he wants and how he feels. Just like he told me he talked to somebody while we broke up, saw them twice, and didn't think it would work. Which made me mad because he said "she doesn't live here so it wouldn't work out" she's away at college, so I'm thinking... when it's summer are you going to try to get with her???? 😑 and obv I mean he hasn't really moved on and neither have I. I think we needed this to grow, I know I have changed, we started young of course, at 14 for 4.5 years.