What to say while breaking up to hurt less?

I am M20 in college, I recent completed 1 year anniversary and my relationship is very healthy.Ever since our relationship started there was always a difference between our feelings, she used to be in very much of love and I liked her and loved spending time with her. I also tried to broke up after 3montha of relationship saying "i don't love you as much as u do" but she asked me to give more time to this relationship.As time passed i also for comfortable and felt like loving her and we had a great relationship, i genuinely care about her and feel attached.

But in last 1 month after our anniversary the thing is I started losing feelings for her I don't know the exact reason, is it because she started being serious like talking about marriage and stuff and I get little bit scared that we are not on same page and I have already given this relationship enough time and I don't think I can reciprocate her feelings.

I am also not doing great in my life i am trying to but I know she have a better future and she should see someone who can give her better life and don't waste more time on me.

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So how do I disclose to her by saying what to hurt her less because I do care about her!!!