How do I (25M) deal with retroactive jealousy? My boyfriend (23M) his ex all of a sudden sent him a pic of them together a few weeks ago captioned 'look what I came acros haha' and he didn't tell me about it. During the first months of our relationship (we've been together for 6 months now) I saw messages from guys he used to hookup with, he did tell them he was dating me so that he wasn't able to meet up with them but I still felt anxious. He went to gaysaunas in the past because he says 'he was curious and wanted to try many things in his younger years'. Every time I think I'm over those things, they all of a sudden start to rise up in my thoughts again which causes anxiety.
Also, every once in a while I start to fixate on the fact my boyfriend once had an open relationship. He has told me multiple times that he doesn't want one and that he didn't like it when he had an open relationship, but he also told me that he doesn't regret having one. When I express my opinion on open relationships, he tells me to mind my own business and that a happy monogamous relationship works for me but that it's also possible for others to be happy in an open relationship.
How can I help myself to stop these anxious thoughts and patterns? My boyfriend has proven himself time and time again but when I don't see him for 3 days or more I start to get anxious again. My doctor has adviced me to search for a therapist.