My parents divorced when I was 5 and my parents never hid away any partners they had.
My mom was main carer so how on earth was she supposed to hide her personal life when I lived with her? It's much easier for the NRP to keep children away from new relationships but I don't see how realistically it can easily be done when the resident parent meets someone?
The OPs son is 12 years old so it's not like he's fast asleep in bed by 7pm and his mom can sneak her boyfriend in is it?
I don't think it's fair that resident parents should have to restrict their private lives and personal lives whilst the NRP can have relationships relatively easily in their child's absence.
I was certainly never traumatised by meeting any of my parents new partners.
The OPs son is 12, his parents have been separated for 8 years so I doubt h a going to be too bothered about his mom having a boyfriend - kids aren't stupid at that age and they know people have relationships. We also live in a time where many children live in homes where parents aren't together and moms and dad's have girlfriends and boyfriends and children live in blended families with step parents etc..... I really don't think it's something a 12 year old won't be aware of or would need shielding from.
I can't tell from your post though OP if your son already knows you're going with a man? Or does he think you're going alone?
Personally I would just take your son along, I don't think in your situation that 6 weeks is considered too soon.