I feel like I should break up with a woman for shitty reasons.
Why are your reasons shitty? Didn't you fall in love with her for those same reasons?
No, I don't really think they're shitty.
It's okay to fall out of love with someone and I would recommend you think very hard if you're really ready to break up with her. She may be hurt with the break up and I would make sure that it's really for the best and it's really with good reasons.
It's not that serious, I got a better deal.
It is serious, you are going to be breaking her heart by breaking up with her. You need to have more respect for this woman and let her down easily and explain to her the good reasons that you have for moving on to new relationships.