Hi and welcome,
I suggest coming clean on your past affairs and that you think you identify as poly .... and suggest an open marriage arrangement. Why settle...
My husband and I have fairly regular and fairly satisfying sex, but I find myself craving other sexual experiences that aren't possible within the context of my relationship.
The quote above and the use of submissive and dominant makes me think you have an interest in exploring the kink world. Is that the case ...and have you tried to get your husband interested in such activities and he was not interested or he's rather submissive himself so it wouldn't work for you.
This too could be a focal point and basis for the poly conversation ...here's what I need/want and you can't/won't provide. Seems very common with the poly and kink communities.
I found that I feel very depressed in terms of my sex life
What have you done with your husband to make "your " sex life better? Out side seeking the oral attention of others. And did that help your sex life with your husband? which could be listed on the benefit side for him if it did. Have you had conversations about this with him ..does he know your depressed about your sex life ? Did you buy any books...go to any classes or workshops...see a sex therapist ......go lingerie shopping together ???
Maybe he's depressed too. Maybe he'll jump at the opportunity to open up.
Lastly is it the sex or all the mental stuff before (lead up) and during ...that whole chemical cocktail ...NRE.