I only scroll this sub nowadays but I'm going to pop back in for this one. This isn't you thinking like a TBM. This stuff is hard and has the potential to be incredibly destructive without a solid foundation of honesty, trust and respect - honesty about boundaries/limits, respect for each other's boundaries, and trust that no one will coerce or step on the other.

If you haven't already had a sit-down discussion on each of your boundaries, now would be the time to do so. These sorts of decisions aren't the thing to just spring on your partner and hope they're feeling charitable. It should be fulfilling for both.

I noticed your post is very bare-bones and seems to purposefully leave out your emotions. That sends a flag to me that this situation is likely causing you significant pain. Please consider that your needs are just as important as his. When you have the boundary talk, I would suggest writing them down. It helps cement them, and provides a reference for if you start to second-guess yourself down the road. Good luck.

I have my own opinions on his idea that this arrangement is better for the kids, but I'll keep that to myself.