Lying to partner to spare her feelings, she mistrusts and avoids me

You feel that you have lied to your girlfriend about certain things in order to avoid dealing with worsened situations had she known the truth. Now you both are to be married but it has come to a point where you think that she does not trust you as much which has caused her to avoid you, more so when her friends are around. With the marriage coming closer, her lack of trust in you bothers you and it hurts even more to have her avoid you, especially in front of others.
Your intention to spare your girlfriend is understandable, however, it is important that you know that it is not your place to make decision for her about her feelings. She is entitled to feel the way she does. What would be more effective here is to have a conversation about it. Put everything on the table. If you are scared of confronting and confessing all at one go, just have a casual hypothetical conversation with the intention of wanting to know her thoughts and feelings on the same. Let her decide what she thinks and feels about it and talk about ways of arriving to a mutual ground on acceptable terms that you both are comfortable with. This will also provide hr an opportunity to trust you.
It is important that you both address such vital concerns before entering into a marriage as trust and mutual respect and regard is the foundation upon which the journey is built and a shaky foundation will not last long.