Just to start off by saying that I haven't previously had "unhealthy" interactions with him, but I did with my XH.
We were sitting up in bed and he was on his phone and I saw on his screen something from someone called "Anna Bumble" (not her real name). I know that when he was on online dating (where we met) that he saved people on his phone as "Name" and "where he met them". I also know that he was on Bumble. So my paranoia kicked in and I started to question why he was talking to a woman from a dating site. But within 5 minutes I asked him about it. I told him what I had seen and why it had concerned me. He smiled and told me to come with him. He opened up the screen, showed me that it was his work emails and that it was "Anna Rumble" (not her real name). He also said he had no idea who she was as it was just a mass email.
Not only was he not at all defensive, he was happy to reassure me, understood why I thought what I did and the whole thing was resolved within minutes. No annoyance.
I'm also pleased with myself that I approached this head on. With my ex, the reaction would have been annoyance that I didn't trust him, that he was having to prove himself etc etc. My DP didn't see it like that. I felt bad for questioning him, but he understood where the question came from and didn't see it as an issue with trust. Quite the opposite because I felt ok enough with him to ask him about it.
This is a huge milestone for me. Not only to approach it head on, but for the reaction not to be to put me down and make me feel awful.
This is worth celebrating.