At ten mths old the babies main source of nutrition should be milk, the best milk or rsthter the normal milk it should have is breast milk, human milk for a human baby.
Formula is fine (two of mine have had it) but it I no way compares to breast m, simply doesn't.
Any father who gave a shit would be happy his child's mother was bfeeding and they should have worked out a schedule of daytime co tsct, little and often as the courts would generally recommend in these circumstances, to make sure the baby can bfeed and have a relationship with their father.