My Parents my boyfriend

so I'm 18, and I've always respected my parents decisions, but for some reason they hate my boyfriend's, he's never cheated and treats me well, but they hate him and watch out for every little thing he does wrong and hold it against him! Idk why but it's constant resently. no body's perfect, There always nice to his face but as soon as he's gone they will encourage me not to see him and try to convince me not to date him. I dunno what to do because I am so in love with him and the thought of loosing my best friend kills me. It makes me feel down being stuck in the middle and I don't want him to feel un-welcome or anything like that...