Why do you feel insecure? Like, do you have specific things that are bothering you about this... If so, it'd be a good idea to look at them rather than the issue on a whole. As relatively speaking, you have nothing to worry about. You've got to remember he's with you because he likes you for who you are, everything else shouldn't matter. But if it does, you need to figure out why.
You've got nothing to prove in yourself, nor should this be a case of you not being good enough. Like I said, if he didn't like you in the first place he would be with you. You should never judge a relationship on your partners experiences from the past. They're irrelevant, all that should matter is the here and now.
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They are the Kings. They are the Queens.
They write the history of the kingdom
and I am something of a devoted Jester.
Earn yourself some easy points