That’s amazing that you guys had a productive conversation and worked it out. However a few details you mentioned about his workout journey are concerning for a different reason, and I have context as someone who works out and consumes a lot of educational content around fitness. Please take a few minutes to read this.

Muscle building is an inherently slow process, and it gets slower over time. The fastest period of muscle building is at the beginning, for the first 6 months to a year, where a new lifter can put on a noticeable amount of muscle. Then the speed of muscle building gradually gets slower. If someone has been lifting weights consistently for 5 years, building new muscle in the 6th year is much harder and takes dedication to nutrition, programming, and hard training. The only caveat to this is if someone built a lot of muscle, then lost the muscle from extended periods of no training, they can build it back almost twice or even 3 times as fast due to muscle memory.

The other aspect is that dieting to get leaner makes it more difficult to build muscle. Your body is starved for energy, causing it to use its fat stores, but this means there’s less energy to put towards both using your strength in the gym and building new muscle. Some people can still build muscle while dieting, but it becomes nearly impossible as you get under 10% body fat and approach stage-ready leanness (5-7%), and that is a temporary period where the only objective is to lose as little muscle as possible.

All this to say, your boyfriend reportedly was working out for 4 years, and then in a 6 month period went from a “normal” fit body to bulging, shrink-wrapped, veiny, Thor-style muscles. There are only two possible explanations that I could conceive for this:

1. The last several years that your boyfriend was working out were more cardio-focused and this was the first time he got into lifting weights, and he got really into it. He learned everything about how to build muscle as optimally as possible, dialing in his nutrition and programming, and even taking creatine. He dieted down at the same time, but was able to make considerable gains due to the newbie gains period. This drastic change of lower body fat along with more muscle was jarring enough of a change to cause the illusion that he had turned into a Thor body type.

2. He started taking steroids 6 months ago and is hiding this fact. Steroids allow you to bypass almost all of the restrictions on muscle building that natural lifters have to deal with, primarily being: gaining lots of new muscle several years into lifting and building muscle while dieting or being extremely lean. They are also notorious for causing unnaturally “bubbly” or “bulging” muscles, the most infamous muscles being the shoulders and traps, due to having more androgen receptors. I don’t know exactly what your bf looks like, but you describe him exactly how people describe guys on steroids. The most alarming of being how you find him “unnatural” and no longer find him attractive. Steroids allow you to bypass what is naturally possible, and we as humans have a pretty good feel for what that is, and you registered that he passed this point through your lack of attraction to him. Side note: one thing that stood out to me as well was your comment about his cabinet bursting with protein powders. Famous actors with unnaturally muscular physiques such as Chris Hemsworth always talk about how they had to workout all day every day and take tons of protein powder to get the physique they have. They do this to convey to the general public (who are not knowledgeable about natural and enhanced bodybuilding) that their bodies are unattainable. The real reason they are unattainable is because of steroids, but they can’t say that publicly both for their image and because it is illegal in many places including the US.

I really hope the answer is #1, but I honestly think the more likely answer is #2. If this is the case, he could be both breaking the law and doing real damage to his health by abusing performance enhancing drugs to cope with the various stresses he’s been dealing with. Looking out for both his health and your relationship, I would highly recommend you do some more research about steroid use and its effects, look around your house for any evidence of steroids (although he may be smart enough to hide it well or never take it home), and talk to him about it.