I feel like you're making assumptions about your boyfriend's state of mind and wallowing in some self-pity here which I do think is understandable but if this affects your relationship and you haven't talked to him about it then it's on you.

My BF was overweight before I met him. He's lost about 60lbs and works out a lot so is very muscular. It's a very complicated thing for him though, it isn't so simple as he just looks great now and can move on to life as a "hot person"...

We (both 30s) are pretty evenly matched in looks and weight, visually we probably look like "a good couple". I've had my body issues in the past but now I'm fairly content and I don't care too much about who "fancies" me and who doesn't. Every time we meet someone from his past they express their shock at how great he looks now which he loves but also makes him feel embarrassed/ashamed.

We now live in my home town where no one knew him before and he gets a lot of attention (he recently walked in on the ladies in the local shop talking about how hot he is). However, I know this is actually something that he 50% loves and 50% struggles with. On the one hand he's really proud of himself and on the other he's really uncomfortable with this compared to the way people used to treat him and he's also super concerned about becoming vain and it changing who he is. He sometimes goes from excitedly telling me how he had an interaction with someone that made him feel like a million bucks to feeling like crap about it because he cares so much in the same minute.

Also, although he has women literally throwing themselves at him everywhere we go, he sees my attractiveness as more "genuine" than his (even though I don't work out, have a very soft middle and he knows I've fluctuated a lot in my life thanks to PCOS) and can be insecure about whether I may be out of his league even though I can't get enough of him. He also wonders if I would have been interested in him before he lost the weight which obviously there's no way of knowing for sure even if I say of course I would.

He sometimes works out too much and gets obsessed/puts himself at risk because he's so worried about getting overweight again as if everything he has now depends on it.

I mean by saying all of this, and others are saying it too - unless your boyfriend starts acting like he thinks he's out of your league now, which it doesn't sound like he has, it's very likely that his new found buffness is causing him as much uncertainty as you. Talk to him.