How do I break up with my gf of 3 years when she hasn’t done anything bad (23M and 21F)

I’m 23M and she is 21F. We have been together for 3 years, we also live in an apartment together, for the past couple months I’ve been noticing that while living together, we have been in a constant state of stagnancy and we just find ourselves either at work with our conflicting schedules now (I work most mornings and she works mostly nights) or if we are in our days off, if they line up together, we just spend our time sitting on the couch and watching shows or being on our phones. There is a little bit of a financial situation where we don’t have the extra money to go out and do things all the time and I understand that even going for a little walk is free and that’s spending time with each other, I’ve noticed slowly that I’ve been losing that spark and feelings for her and I noticed that I’ve been getting into bad habits, I gained a lot of weight and I’m realizing it now and I recently started working out again consistently around a week ago but she doesn’t want to work out with me, she just spends her time on her phone mostly or watching tv shows. We’re both introverted people but I find myself having more fun being at work or with my friends and started realizing I’m happier and I laugh more when I’m not home. This is also entirely my fault, she is such a great and genuine person that cares for me and will always tell me she loves me whether that’s in person or on the phone or in text, she has never cheated or even batted an eye at another guy in any form of attraction and she has only ever had eyes for me. I, for one, have started to neglect the relationship subconsciously by not caring as much and even thinking about it, after the honeymoon phase of the first couple months of us dating, I stopped putting in the effort to be a good boyfriend. We don’t have fights but I just feel like I’m not worthy of how good of a person she is and how sweet she is to me when all I do before I started working out was either work, play video-games or just sit on the couch with her, I’ve stopped putting in the effort completely and that’s how I am in relationships when I get bored, I’ve just completely lost feelings but I’ve told her before that my greatest fear in life is to look her in the eye as the person I love the most and just tell her I don’t feel the same as I used to anymore. I feel like this is something I need to work on whole I’m alone and truly find the reason of why I’m like this and I just don’t want to keep wasting her time and I know people just say “get the balls to break up with her”, I want to, to make her live her life and be with someone who will actually put in the effort in the relationship but I just can’t get myself to break up with her since I don’t want to see her heartbroken. I don’t know how to go about this break up and I need help on how to do it, I just feel the best course of action is to let her live her life without me hurting her and not putting any effort in the relationship and for me to figure out how to remedy my issues while I’m alone. Can someone give me advice on how to handle breaking up with her in the best way possible?