Thank you in advance for any help or advice you may have. This is new territory for me and any input is appreciated.

I (25f) have been in a long term relationship with my fiance and Daddy Dom (36m) and have recently started seeing another dominant (33m) a couple of times. We have been been poly for a very long time but I have never had any partners that I've gotten very excited about and it normally only lasts a couple of meets. And has never been kinky or had any power exchange. This time is different though. Honestly the new Dom I've been seeing is amazing and fullfils a lot of kinks that my Daddy doesn't particularly like or do often. I've been trying to really reign in on my excitement and not brag about how amazing these couple of meet ups I've had have been but my Daddy is still feeling very hurt. To be blunt this new Dom is much more experienced and my Daddy is feeling very insecure. He knows that I have no interest in this new Dom beyond play and that I'm not going anywhere, but he's still feeling left out and challenged by my new Dom.

I'm looking for some tips to make my Daddy feel more special and secure in our dynamic, and less threatened by this new Dom. Also, since this is still so new we have had trouble coming up with ideas as far as limits and rules for each of them so they aren't stepping on each other's toes. I have made it clear that I will only have a DD/lg dynamic with my Daddy and will not even come close to that play with this new Dom, but was wondering if there are any other common rules (like no marks, ect) that have helped anyone? Basically any tips to help my Daddy with this new partner would be greatly appreciated because we both want this to continue and are struggling with these new feelings he's having.

TLDR: Looking for tips to help my existing Dom with feelings of jealousy and insecurity with a new Dominant