boyfriend's Parents Becoming a Major Issue...

Hey I’m Sarah and I am 18 and I have been dating my boyfriend Austin, who is 19 soon to be 20, now for 5 months. Everything between us has been going awesome except with his parents.Every since we made it official they have been saying rude,uncalled for, and really untrue stuff about me.I have never insulted his parents or gave them a reason to hate me but it seems as though they are making up reasons so that me and Austin break up once and for all ,which I think is messed up.In fact, we almost broke up once because his parents really got to me at one point and I got overwhelmed so much that I wanted to end it because I just couldn’t take it anymore.However, we ended up getting back together because I realized that if we broke up not only was I going to let them win but I would be making a major mistake that could effect the rest of my life because I truly adore and love Austin.Even though, Its been only 5 months , I feel us getting more serious to a point where I could see myself getting engaged to him someday later down the road because he has mature qualities that a husband has towards his wife.But his parents just keep getting in the way of what we have for no reason whatsoever.For instance, they call me controlling and that I’m molding him to be something that he has never been.I find that odd considering I love who he is and never once told him to be something he wasn’t and as far as “controlling” goes I don’t control him, when he goes out with his parents locally I don’t smother him with calls or tell him when to come home.In fact, I consider myself easy going and I tend to take life one day at a time and I don’t rush anything.Bottom line is I don’t know why they constantly say negative untrue things about me when I’m not in the same room as them.I just want his parents to accept me, that’s all I want, they don’t have to love me or even like me but I wish they would just accept me and take their microscope off of me and Austins relationship once and for all because after all we are both adults and can make our own decisions.We just need some advice with this still current issue because this is becoming very hard on the both of us.I don’t know if their doing this rude behavior because he is the youngest in the family, with two older siblings or because he is their only son or because they don’t want him to date while hes in college.But all I know is any advice would help us both especially in this confusing and hurtful situation…