I sometimes don't feel like I'm enough for my boyfriend. Is it reasonable to feel like he will leave me for something better?

Let me clarify; my boyfriend and I have been together for a year as of October 4th. I love him and am in love with him. As far as I can tell and feel, the feeling is mutual. Which is a good thing, lol. But some days, I feel like I'm not enough for him. I mean he is a total fucking 10/10. Absolutely gorgeous inside and out. Just an absolute star in my otherwise dark sky if you get what I mean. I feel like, my body isn't toned enough, that I'm not manly enough, that I may be inadequate in bed, I mean just all these fears. Other days...most days, these feelings aren't prevalent. It's not that I'm afraid of losing him. It's that I'm afraid someone better looking will come along and take him from me. We've been through so much, I mean he stood by me when I was broke and not a very nice person. And now that we're doing better and are on the way to being successful, like we've talked about buying a house and starting a company and having kids, getting married etc...but I don't know. Should I hit the gym? Should I try to spice things up in the bedroom? What doesn't help this is that I work intense hard labor in construction, so I am constantly sore, constantly hurting and tired. I mean, I slipped a disk in my back 2 weeks ago and feel like a cripple around him. He's 20, I'm 23, for the record. I don't know. I don't know what I'm feeling or even if it's rational to feel it. I just want to know that I'm enough for him and that he's happy. Because he's enough for me, and I am happy with him.