Don't trust my sister my mom said I shouldn't say anything?

My sister has always been attention seeking and unruly I recently started talking to this new guy and I really like him a lot he's the sweetest guy I ever met but everytime we are video chatting she always tried to be on camera she even said in a sarcastic way that it looks like we are not talking anymore like she serectly hoped he stopped talking to me. I am overweight and she is slim so she thinks she has some advantage over me with guys my mother doesn't control her behaviour she's wild smokes and drinks and wears reveling clothes

I don't trust her around my boyfriend because she has always had this behaviour like she is in competition with me. I told my boyfriend that if she tries anything he should let me know because I had issues in the past that one of my cousins flirting with my ex. my mother said I shouldn't say anything to him but I don't take her advice on anything because she never defended me when my cousin flirted with my ex so I don't trust her. i told my boyfriend about my sister and he said he understands and that he will let me know if anything happens is it wrong that I brought it up with him? I just want a honest relationship with him he even told me himself that he has male family members he wouldn't bring me around because how they're are he said this before I brought up any of this up I really like this guy and me and him had similar break ups we were both cheated on and we both are looking for the same thing in a relationship.
Don't trust my sister my mom said I shouldn't say anything?
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