Partner's 23 year old dependant son

Hi 

I notice someone mentioned their husband's recent diagnosis so I figured this was ok to bring to the table. My partner's son (I'll call him Tom) has been diagnosed within the past 12m. He has had and lost 2 jobs within that time and has no friends. My partner has a full time job and also trying to renovate his home himself (due to financial constraints). My worry is that my partner expects his son's behaviour to change over time. Tom sits on his computer all night and then can't get up in the morning but even when his dad discusses this with him and Tom agrees it's not right, he does it again over and over. He doesn't contribute anything to the home and appears very arrogant and a know-it-all. I must sound awful but this is how it is. He is deceitful and tells lies. I can see the toll it is taking on his dad and I would appreciate some advice about how to deal with this. Is tough love a no-no with autistic adult children? I feel he takes his dad's kindness and patience for granted and has no incentive to do anything differently.