Partner of 10 months just told me I'm too big?!

Hiya - throwaway account because people know my main:I've been in a really good relationship for just over 10 months now and I have never been happier. But our sex life has dwindled to only oral and hand stuff for about 5 months now and it's been really worrying me. I've tried bringing it up to my partner and he's always made excuses like he wasn't feeling great or there's people in the house and he didn't want them to hear. But it came up again today and he finally told me that my penis is too big for him (8.5-9") and it's hard for him to take, even though he says he loves bottoming. I have honestly never been happier in a relationship and I can honestly see myself having a proper future with this guy - but he has told me that bottoming for him is a lot of fun and the thought of not doing it anymore scares him. We're both still quite young at 20, and we should (in my opinion) be having sex 2-3 times a week. I don't mind bottoming but we both prefer it with me topping him. So I'm desperate for some advice. I want this relationship to work, and I want our sex life to be active and exciting like I know he wants it to be too. What can we do to keep our relationship exciting and stimulating for the both of us? Thanks in advance!