I have always dreamed of what it would be like when he got sober and now that he is I still feel like I'm not enough.
that's a very revealing statement. his using was never about you....and it had absolutely NO bearing on YOUR self worth. nor is his choosing to get sober a reflection upon YOU. HE owns that....HIS addiction, HIS recovery. and let's go a step further....HIS life.
you must find your own value, believe it and commit to it. his latest thing with online hookup sites - that's him trying to USE to feel better, different. it is disrespectful for sure, but not a comment on you not being good enough.
you are pefectly enough exactly as you are. you said you were committed to the relationship....as if it is a separate entity, apart from each of you. after 7 years together, the past few months are the first time you've ever experienced your BF out from under the influence. now he's extra needy, and overly focused on sex and sexting and texting with another girl - taking it too far. DTF means Down to F*** - that is not some harmless or inconsequential statement. and doesn't sound very "committed."
probably best to be straight up and tel him what you know AND how you feel about it. if you get anything but remorse and a humble ownership of the wrongness of his actions, then you'll have a clear indication of his motivation.