transparency is a big key, talk to him, ask him if there's something that u shud know even though u might not like him. cuz i get it, not matter how much they tell u they love you, if they lied once and did shit that they weren't supposed to, you assume they're most likely to repeat them. lastly observe, did they learn from their past mistakes, has he stopped keeping things and tells me everything.

but i see my partner is lying to his friends and sometimes to his parents, and i overthink what if he is still doing the same thing to me..

hey its okay, i feel you, im a woman myself and you do have that overthinking at the back of ur mind, being with someone who doesn't hesitate before throwing in a lie is hard and i get it, he lied to you once he can do it again, but u gotta go out of yr way to make sure, and no im not saying by being suspicious, by behaving in a way that he doesnt feel the need to hide anything from you. by asking why he actually lied cuz sometimes people do lie because they think telling the truth wont do them any good. so just let him know that doesnt have to hide anything from you