You'll never ever know if a person is sincere. Only he would know. But since the two of you are official already, I think you should trust him. Trust is very important in a relationship. And he said that he wanted you to be his girlfriend. So why not just trust him and see where this goes? And you said he didn't just say that so that you would bed him. At least that's already cleared. There's not much left to worry about is there? You shouldn't let past failures stop you from making this time a success. Good luck!

Actually how long have you known him? Do you know him very well? You only said you've been dating him for a month.

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Clarity of mind means clarity of passion too; this is why a great and clear mind loves ardently and sees distinctly what it loves. -- Blaise Pascal (1623 - 1662)