Unless you have some proof of this it's unlikely it will have any effect other than to make you the judge think you're nuts to even try to bring it up.
Under the rules governing the conduct of attorneys in New York it may be necessary to remind you that this answer could be considered attorney advertising.
Custody analyses are complex and involve many factors. While the ultimate decision is required to be based on the best interests of the child(ren), there are as many interpretations of the statutory factors as there are judges. Equal sharing of custodial time is not the only possibility or consideration. Before committing to any plan of action you need to learn a great deal more about the wide range of factors and the vocabulary of a custody order: legal custody, physical custody, and residential custody. Bisexuality itself may not influence the custody decision, but it would certainly suggest certain terms and conditions that limit his behavior while the children are present and, depending on the strength of your evidence, may reflect negatively on the quality of his decision-making ability for the children. Nothing short of a consultation with an experienced family law practitioner will meet your needs. Be prepared to pay a reasonable fee for the valuable information and advice you will receive.
Best wishes for an outcome you can accept, and please remember to designate a best answer.
This answer is offered as a public service for general information only and may not be relied upon as legal advice.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.