Advice on jealousy
I am a formerly monogamous Bi/Pan male, currently in a relationship with a poly-identifying Pan Non-Binary Person who I love very much. They have introduced me to poly over the last year plus (we will have been going out for two years in a few months) and I have even recently gotten a secondary bf with my primary's support. The problem is this: I am undoubtedly in a poly relationship, but I tend to think like a monogamous person, complete with jealousy. Also, I am fiercely private about my love life (except when my partners ask, of course) and often actually very sex-negative in my thinking in the abstract, especially when it comes to casual sex.
Recently, my primary went away for a week to a conference (of which only a few days have passed), and when they asked what boundaries they needed to abide by, I told them that being vocally emotional and kissing were fine but I was uncomfortable with anything else. Today, while we were talking on the phone, they told me they had made out with someone at the conference who was very chilled and ok with the boundaries we had set, and asked how I felt about that. I froze. I felt uncomfortable, and unhappy. Then, of course, I felt even more unhappy with my reaction because of the fact that my partner had followed the rules, and yet here I was reacting badly to it. This is the first time they have done even that much with anyone else while we've been a couple (apart from a few crushes and pseudo-dates) and I feel bad about that because I currently have a second partner who I have done everything short of penetrative sex with, and my primary has always been supportive and loving throughout. I have often called myself a hypocrite, enjoying the benefits of my partner's ideology while preventing them from acting on it due to my jealousy, although my partner has often said that they don't see it that way.
However, I think I need help. I want my partner to be happy and poly, and I would like to find happiness in polyamory myself as well, but times like this make me really worried that I won't be able to handle it no matter how much I want to. Does anyone have any advice, particularly people who have "converted" from monogamy to polyamory themselves?