What you don't tell us is what neglect means. Do you go on lots of dates with the gf and never the wife? If the gf and the wife both are having an emotional problem, do you ignore the wife and focus ob helping the gf? These are behaviors you can choose to change if you want a strong marriage. If you don't, maybe it's time to start letting go of your wife.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.