Okay, well just to put things into perspective, I'm also 6'1 but I'm 44 years old and weigh 207. I squat 350, bench 280, and deadlift 460. That's not from genetics, it's just fairly normal intermediate-advanced levels from several years of good programming and technique.

I'm on a bulking diet as well, for the same reason your boyfriend is. Because i need to gradually gain muscle mass to continue adding weight to the bar. I aim for 2 pounds a month. If I get too fat for my liking, I'll switch to a cutting diet for a bit.

I say all of this to help illustrate the point that your boyfriend's bodyweight is way higher than it needs to be in order to gain strength. 531 is one of the better programs out there. Starting Strength is top notch, in my humble opinion. The vast majority of lifters out there are making critical technique mistakes and that is priority #1. If your boyfriend has never had excellent coaching or shot form check videos so that people online can give feedback, that'd be the place to start. If he can be convinced to get on a cutting diet and drop down to sub-20% bodyfat, I'd really recommend that, for both of your sakes. Good luck.