my exgirlfriend hired the same lawyer as my other ex for my new custody case is this a conflict of interest

The answer is "no"--as far as YOU are concerned.  Presumably, both of them have interests which are adverse to you.  If, based on his prior representation, that lawyer has information which can be used against you, that is unfortunate but it does not allow you to disqualify the lawyer.  Only if the lawyer previously represented YOU, that would be a conflict.