Under these facts, it would not only be reasonable, but recommended.  In addition to asking for full custody, you should also seek restrictions on his visitations and ask for supervised visits.  If he has attempted suicide in front of the child, this should be a huge factor for the judge to rule in your favor.If you don't already have a custody suit pending... then that would be your starting point.  File the suit and ask for orders that grant you custody and restrict his periods of visitation.  If you already have orders in place, then you would need to file a motion to modify those orders-- citing to these recent events as a basis for the modification.