As someone who has had 3 women in my life who have played the role of Mommy to me, allow me to sate your curiosity
Although,keep in mind,everyone who has had a relationship with a GF/Wife that is also Caregiver will bring their own opinions and responses to the table as well
Out of the 3 women who have Mommied me, only 2 of them were my official GFs
With both of these relationships we kept Baby and Mommy time and BF and GF time separate from one another. At first it's a bit awkward, kind of like being in two relationships at once; one as BF and GF and the other as Mommy and Baby. Eventually though, the dynamic gains a sense of normalcy and balance, to the point at which Baby and Mommy time becomes just another couples activity or another emotional layer to how you connect with one another
I personally have never found these relationships to feel weird, and our adult time has never conflicted with Baby/Mommy time or vice-versa, but then again, my relationships have always been more emotionally charged as opposed to sexually charged and I have always viewed my AB side as a part of who I am and as a lifestyle choice, it has never been a sexual kink. Furthermore, as a demisexual, sex has never been a high priority for me, I can count on one hand the number of times I've had sex and my partners have been largely the same way. My 1st Mommy/GF was a much more emotional person, she just wanted to spend time together. My current Mommy/GF is the same, she is also a little bit asexual, she has only had sex once or twice, found it to be boring and too exhausting for its own good and she has told me that she would much rather spend her time cuddling me on the couch as either a Big Boy or a Baby as opposed to having sex anyhow
That being said, many ABs have healthy adult relationships with their Partners/Caregivers that include sex and I don't see how having a healthy relationship with both a strictly adult side and a not-so-adult side would impede anything; it's all about finding balance and having the best of both worlds. The way I look at it, sex is a Big-Boy activity, it's the furthest thing from my mind when I regress, my Mommies have felt the same way, so it's always been easy to maintain separation between the Baby/Mommy time and the BF/GF time.
Of course, at the end of the day, finding the right partner is paramount. I think it is easy for an AB to not be bothered by the shifting dynamics in this type of a relationship because nearly every AB I know, myself included, has learned to compartmentalize the two halves of the whole; we are babies/littles when time allows, but we are adults too with adult responsibilities. If you can find a partner who can compartmentalize and view this in the same way that you do, then you'll find the dynamic/relationship you seek