Your spouse has a right to expect a REASONABLE facsimile of the person they signed up for marriage with, save for the normal ravages of father time.  

Obesity is an erection suppressant, both from being with an obese woman or by being an obese man.  Anyone who thinks a man can get it up no matter what, as long as he loves his wife,  doesn't understand the first thing about male physiology and  arousal.  

No one should ever blame their spouse for their bad health and fitness choices.  In the end, you're hurting yourself more than them.  You're also being a potential drain on our taxpayer-funded healthcare system. 

You can have excuses or results.  You can't have both.