Why do I feel like I'm not good enough for him and like he secretly dislikes me?

I am noticing some very scary things in my life here recently. I just came out of a 17 year relationship and started dating a man whom is 9 years younger than me. We have known each other for 2 years, and over the past year we have spoke daily/nightly.He admitted that he loved me back in December. We made our relationship official in March. Things were going great, and according to him they still are but I am finding that I am constantly trying to figure out what he sees in me. He tells me he loves me everyday, he is always talking positive about me when we are out with people. Our sex life is amazing. He tells me I am beautiful and he is always talking about our future together. But even though all of these signs of his interest in me are there, I keep getting the feeling that he's too good for me, and then I close up and get mad and try to find reasons that could mean he is losing interest in me? I don't understand what is going on here. I feel like I need constant reassurance from him and I know this could put a strain on our relationship. I love him so much, and I hate doing this. What could be causing me to act this way? It seems every other day we are talking about our feelings and how my behavior or his behavior makes us feel and it still keeps happening. Help!