Biblically, there are only two situations in which it’s okay for an adult to have their lips on a woman’s breasts: if they are a man and woman married to each other, or for health reasons, if they are in China or similar country where it’s culturally and institutionally accepted to breastfeed adults for medical benefits. Anything else will feel too sexual.
Bottom line is, we move the goalposts and challenge God’s decrees if we fail to be above reproach by misinterpreting Scripture to our fleshly pleasure.
God is very concerned not only with the letter, but primarily the spirit, along with the setting, context and wider social effect. And any kind of nursing outside marriage has the spirit of cheating and necessarily carries an imbued sexual tone, unless occurring in said culture where adult nursing isn’t offensive but rather promoted in the context of medical care.
In the latter scenario, the presence of witnesses restricts the likelihood of sexual sin.
Let’s honor the Lord by being above reproach. God bless.