Is it morally okay to leave a long-term relationship for a better match?

perspective wise I could see it hurting a lot. thats not really the purpose. they keep themselves stuck in this relationship she obviously hates being in. a girl I knew her 15 years ago comes back I know her better and she's probably the better match from a logical stand point. but its like my feelings are so stretched and feel mangled with the other girl. I dont even feel like talking to her but I know its at a point that I could just say how I feel and we'd immediately run off on a date. but her boy toy has all these dudes surrounding us because he's too weak of a human to handle any of it on his own so its difficult to get a word through much less figure out how to say it because they know somethings up between us but they dont know what. she knows this. I dont get it. if I know the game but not the feeling does that mean I quit and move on? whats the best moral route here?

Is it morally okay to leave a long-term relationship for a better match?
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