should I push him or should he get legal help

Hi all what would you do! 
I'm pregnant and almost due
My partners ex from 5 years ago has facebooked him with photos of a almost 6 year old girl 
Plus a massage (sorry I didn't tell you) 
She wants to meet up, my partner wants dna as the reason they ended was she cheated she claims dna was done with the other guy so the 5 year old is 100% his 
I personally feel sick but with that said growing up with out my father I missed out on a lot so I said he should try and see her 
He thinks I'm crazy with out the dna first 
I'll stand by him 100% 
She will be in town next month 
He asked to bring me along she said no so 
I told him I understand that 
He don't wanna go alone but the other chick is even saying no to him bringing his mum 
Should he legal help or should he just go
I don't wanna be to pushy but I don't want him to be hurt in the long run and I don't want that little girl to be hurt either   (She is so young)  
I would like to add my partners ex and his mum always got on ect till she moved away 
And my partners mum dose not no why they split