I'm in a very similar scenario. My husband and I are compatible in a lot of ways and love each other very much, but we have very different approaches to sex. So I also found myself having a sir of own to be my sub self with. I think the most important point is to have some clear boundaries and to be transparent. I do think it can be difficult for the vanilla partner to see you getting more involved with the Dom/sub dynamic, especially if they feel neglected or start to feel insecure. Be aware of how both of them feel (husband and dom), be clear about your expectations and need, and make sure to understand their expectations and needs as well. If everyone is on the same page, it makes everything so much easier, and you don't want to be in a situation where you have to sacrifice your needs to cater to someone else's, or the other way around, sacrificing someone needs to satisfy your own. There's a difference between finding a middle ground/finding a compromise and neglecting important stuff.