Is this in the normal range of male behavior?

Masturbation is addictive. Too much masturbation can lead to prostate cancer, so he might want to slow down a bit. Masturbation is also beneficial to health. In this way too much is bad and not enough sexual activity can also be bad. It is easy for a guy to get addicted to it, but convincing him to take a break from it can help him too, as too much can lead to irritability. He will also find sex more enjoyable if he takes a break from masturbation for a while. But yes, is normal.

What defines masturbating 'a lot'?

Leaving seman stains on the carpet? No, that isn't normal if they are in fact seman stains. Most men do try to clean up after themselves. How do you know they are stains from him masturbating?

As for the link to prostate cancer from what I just read there may be link but depending on age the risk factor may increase or decrease. There is still a lot that is unknown. It is still speculation and nothing is conclusive.

When I first saw the title, I thought range, did she mean distance, perhaps a couple feet ?

But no leaving stains on the carpet is a person who has no self control, no self respect and no good hygene. Basically a slob.

Also what do you mean by a lot? Once a day, 10 times a day?

Addiction can effect normal sexual behavior, where without the tighter feel of their hand, they have trouble keeping an erection. But just the fact he is not cleaning up after his self, well perhaps time for a new boyfriend.

One word sums this up; Grim.
NO this is NOT "normal"

No he sound like he's nasty. Why don't he clean up his place instead of letting it get all over. Gross

Wait wait... on the CARPET? Whoops I just completely missed that bit assumed it said 'sheets'. Yeah I have to admit that does sound pretty messed up. Are you sure they are semen stains?