Gosh I know, well to some extent! I have pretty bad insecurities as I'm guessing most people do and because I haven't known my vet for very long I was initially very paranoid and needy about what he was up to and if he was seeing someone else. However he deleted his dating apps and told me and then I deleted mine and he has never given me any reason to believe he has not been monogamous. This is another reason why I'm happy to bypass the commitment thing and calling him my boyfriend. I know you said that he was changing his picture on his dating profile? This is where boundaries probably come into play, you should say I am not on dating sites because I am committed to giving 'us' a go and seeing if we could be something in the future, I would like you to do the same, if you cannot commit to doing that then I will leave and move on. If he doesn't do it, you have to stick to your boundary otherwise when you try to put other boundaries in place he won't believe you if you don't stick to the ultimatum. Does this make sense?
It's ok to express your wants and needs, just be sure to make sure they are absolutely essential because if you say you will leave if he doesn't do something then you have to stick to it.