Good day, am in a relationship I really want to end, because I already know it won't end in marriage, apparently my girlfriend want me to marry her and she want it so badly.

My question is how do I end it without causing a serious damage?

Just do it gently, and take all the blame, and tell her what a great catch she will be fore the right guy. No way that you avoid the pain and misery of being dumped for her.

Have the good sense to disappear after you do, forever.