My mom passed away and I don't know what my father wants, needs or what to do to help him. How can I best help him and communicate?

Maybe you could look for visual cues rather than verbal ones. If your father is like mine, then he is rather stoic and less interested in "sharing" feelings.
Look for signs that he may be depressed and find things he likes to do. Can he go on outings....these seem to cheer up my Mom. Does he have hobbies or people he likes to visit. If you are both greiving, it would be great if you both got out to be around other people.
When and if he needs to talk about your Mom he will bring it up..just wait for those cues. It may still be really painful for him to talk about your Mom and, as you said, he may think he needs to be strong for you. When both people are in pain, it is hard to think clearly.
Time is a great healer. I think that it is a very human thing to think that when we stop greiving for someone they are somehow forgotton. I think that is why we greive for so long over a loved one.

check with a hospice in your area. they do offer support for grieving families before and after the death of a loved one

My mom died 7 years ago, and I still get emontional when talking about her, it's ok. Now about dad, my dad wanted to be left alone at his house, he did some hobbies but mostly stuck to himself. I poped in 2-3 times a week. bringing food or, just stopped in to say hi and tell him about my day at work. He seemed to like the visits as long as they were short, he's not much of a talker. When he started saying "What are you doing here so often, I started coming once a week but called or had my brothers call. We set up who would call on what day. But after a year there was one week we did not talk to him for three days so I stoped by to find he had had a stroke, and was on the floor for 2 days. He did recover but never was abel to go back home so he lives with me, and is still not a big talker. But we have some good conversations when it's just the two of us. So keep communicating even if he does not seem interested.