I think Dan actually likes to think he is an Alpha, but when he meets men like Lester and Byron, he is at a loss. It is one thing to power someone physically around, but people like Lester and Byron not only out-think him, but then lord it over him. People like Jesse and Peter are who he normally has no problem controlling as they are just users and bottom-feeders. I think Dan feels, in many ways, less than people like Lester and Byron as they are smarter than him and he lacks complete confidence in his own intelligence.
He always has to build himself into it, or talk him self into it or have Sarah boost his self-image when he is looking at jobs and ways to save his family. Sarah has to convince Dan that he is a great head-of-family before she eventually questions him being capable of that position as she has been actually taking on that role for months, if not years, and that is not what she wanted in life. Yes, she wanted to be a partner but also controlled in some ways by the masculinity of her husband and what she misses as she finds him an apartment in Chicago, or finds him ads for jobs in the paper, of acts as the bread-winner in her own job as opposed to Dan.
She runs her household and she always wanted Dan to do that and he won't, but Lester will and does and that turns her the fuck on as that is what she perceives as masculine and sexy and Dan is, just -- quite frankly -- missing that. I have though about it, long and hard and this answers many issues presented to the reader of this most recent chapter. Sarah is tired of asking Dan what to do and he hems and haws and is really milque-toastish and indecisive. Lester doesn't need to be asked, he tells hers what is going to happen and then he does it, causing Sarah to melt into a puddle on the floor for him instead of her husband.
Lester tells Sarah that she craves him and she is wet for him as she thinks about him and his cock throughout the day, at home and work. He asks if she has ever been as affected by Dan as she is by himself and she tells him, never. Not like she is with Lester. It no longer becomes about just the cock size. "Who's the better fuck Sarah, me or Dan?" Without hesitation she cries out, even now, in front of her husband, "you are Lester!" He asks, who owns her pussy and then who owns her as a person and she answers, "You Lester, you own me!" once again, in front of her husband.
There are only two questions left to ask in front of Dan to solidify himself as the head of this household, displacing Dan, entirely. They are, "Who would you rather make love to, not fuck, if given the choice and do you love me?" Maybe when these questions are asked and answered in front of Dan, his heart breaks and he attempts to hurt Lester again, Sarah will stand up and defend Lester, pushing her husband away, before she takes Lester to his bedroom and locks the door to keep Dan out.
Knowing all this now and able to juxtapose this argument, I think Dan is perfectly right in just where he has them.