Advice for a struggling step mom

I need some advice for my 2 and a half year old step son. I just got into a relationship back in august and my fiancé and his ex had just separated and I’ve been in my stepsons life since then. I have him almost every single day and im the only person he goes to. I bathe him I put him to bed I feed him and change him and sometimes I think to myself it’s too much. I’m a full time student and I’m about to get a full time job and I’m scared I can’t handle it all. I worry that I won’t be able to handle my step son when he’s crying and I’m worried he’s behind on his speech and I feel like I don’t have a say in his life but honestly I see him more than his parents do and they don’t see what I see and I just don’t know what to do because they don’t listen to me. Any advice