I need advice very badly 😩

So long story short, my ex left me for his ex back in September. It hurt me really bad and I’m still not over him I thought I was then I seen him for the first time since we broke up the other day and it just hit me all again. I’m with someone else now he makes me very happy and treats me with a lot more respect but it’s just different it’s not the same. I don’t wanna be with him if I don’t really feel the same deep down inside so what do i do. Do I tell him I’m not ready for anything. If I did that I’d feel like I lead him on idk what to do