He's just super desperate not do die alone and to look like a
mature adult. He's willing to be Khet's toy because she's the last girl he'll ever have the chance to be with. The marriage was a desperate but easily predictable act. He proposed to Panda just to make her stay even after their relationship went down the toilet and his parents have most probably been nagging him to get married and settle down. Khet (from all we know) is a white trash leech, he doesn't trust her judgement on things and doesn't trust her with responsibilities. She works [constantly changing amount] of days a week and has income enough to allegedly only pay Hulu or help with (((bills))) and plays skyrim in her ahffice in her spare time. She's not allowed to shop by herself and with the introduction of the exercise bike doesn't even go to the gym. I'd assume that every misfortune that happens in the Burnell household is Khet's fault, because Dark had nothing he could do

and the bottom line is it's her fault.
Of course, there are benefits to Khet. The 'dual income' effect that Dave was bragging about, free maid and cook services and bragging rights to call himself mature.
The depression, as most things with DSP, winds down to having no money (to blow away).