how does one stay the same?

Ok so like this is bad.. When I like someone say someone I am friends with since this is the deal...I am so open and out going and I don't care if I do something that gets them irritated..It isn't purposefully done but I don' care as much as I would if I was in a relationship with them. When I am in a relationship I clam up. I am afraid to make a mistake or to get them mad. How do I not do that. Because the reason someone likes me is cause of how out going I am. (So I would think) But that all changes once we are official. I want to be able to stay the same with being out going I like my personality.. Any advice?