My parents were married for 48 years and my mother just passed away so now my dad’s alone. How do I deal with my dad being alone all day?

All the above are wonderful options. I have just one more to add to the mix. Ask him what he'd like to do. You can start with opened ended questions like, Dad if you could do anything what would it be. No matter how impossible the request may be (let's lay he wants to go to the moon) you have a hint as to interests (interested in space exploration). If able you can get him to help you out around the house. People like to feel productive.

Hi Kathy~ Without knowing all the particualars involved about your Dad, It seems quite understandable (to me) i he would respond this way. To begin, he has lost his life-time partner of 48+ years, amd that can be quite difficult to deal with...He also may now feel a loss of independance, as moving in with you-or even anyone (in-fact)..
Perhaps senior dayc are will be an option-for him to meet others, have the opportunity to socialize, and possibly to somewhat vent, There is a good chance he may even meet other people that are in the same boat as he.
Another option would be grief counceling..Hospice is an excellent organization to hook up with, and there are others as well..

Life does go on-amd we have to make the best of the cards we are delt.

My condolences-to you and your family-and I hope you are able to resolve the situation with your dad. This forum, is a good place to start.

Best,

Hap

Get him something to do. Places to go, a senior center, VFW, any kind of a Peer group of people he can relate to. Teach him to use the computer, if he doesn't know how, get a webcam, skype, expand his world at home and outside the home.
He's not dead, just old - still got a lot of life in him if he goes for it. Encouraging him, reassuring him and letting him be as mobile and connected as possible are good moves.
Keep him Moving, and get him phys therapy if he's unsteady - it helps, and gives him something to look forward to. Again, just fill his time with positive and productive, healthy activities.
Hang in there, it's very tough on them to lose a spouse at that age.