Aibu to ask ex-p to meet his new p, as she is looking after ds?

[Costypop]

I've got an 8yr old DS, his time is spent 50-50 between me and his dad. However DS has been coming home lately saying that Daddy's new girlfriend has been looking after him for the day. At change over dad is always there. This GF it seems is looking after DS 1-2 days per week and whole weekend day and a day in the week doing a school pick up. I've no problem with this as infact dad thinks good parenting is sitting DS in front of the Xbox playing call of duty, where The GF takes him out on his bike and plays with him. In fact I actually want the ex to move in with GF as I think it would be better then where he is at the minutue (house share)
But I've never seen her! Not even a glance, would it unreasonable to force a meeting? At the end of the day she seems to be a big part of my sons life now

Ex-p was adamant to meet my p. (not that turn out too well-read per posts) but I feel is hiding his GF from me, I don't not trust his parenting one bit ATM as it seems my son is being past round for one person to another when he is with his dad. I am currently working with the school, and solicitors to get full custody. I would rather rosulve any issues and work though them with the ex then stop him having a relaxed relationship with his son. But my son comes first

Oh when EX-p met my P I and P said it was fine straight away, even though the ex didn't ask very politely, lots of shouting and swearing down the phone at me