Er...I still don't get why you can't tell the kid's dad about the panic attack.
I think he needs to know.
I don't see how knowing about the panic attack says anything about you knowing anything about how the mum died...in fact, being triggered by a car journey if you think your mum died in a car accident makes heaps of sense.
And that kind of anxiety about separation makes sense however a parent dies.
As for the suicide...I don't think there's anything much you can do except have your explanations ready for if Mo finds out while he's still little...you know, the depression makes you not think straight stuff.
I'm curious to know what you have read about kids whose parents suicide, especially at this kid's age, that worries you so? I am not quite sure what your specific fear in relation to Mo is?