I can't help wondering, would you all be happy for your dh's to have such close relationships with their mothers?
I have seen lots of posts on here wrt dh's relationships with MILs and the consensus has always been that he should break free of the apron strings and that wife/children are his family now.
I don't think there's anything weird about having a close relationship with your mother (I personally don't but my sister does), but I think that there does come a progression in life where we move away from our parents and start our own families, in reality in preparation for the fact that our mothers won't be there one day.
If things are difficult with your dp, then that needs addressing, but if you found another man who wasn't like your dp, would you be prepared to change the relationship you had with your mother then? Because tbh I think that to have a successful relationship it would be necessary to do so. I would be mightily put out if dh was discussing all his life-changing decisions with his parents rather than me, and equally I think he would feel the same if I discussed things with my mum rather than him.
I think you can still have a close relationship with your mum, but I think it's important to move away from her as being your best friend - she's not your friend, she's your mum.