My deepest condolences.

Nothing in this scenario is your control. Motorcycle riders are controllers by nature and this affects all of us to varying degrees.
I've lost friends to motorcycle mishaps (can't call them accidents) and military mishaps.
I've buried a daughter.
I've licensed people to ride motorcycles, and learned after a certain period they were somehow killed on a motorcycle.
Summary: dealt with this many times.

My technique:
- allow grief to occur.
- set aside a period of time for grieving.
- as mentioned already, KNOW that the person you've lost wouldn't want you to stop doing something because that's what got them.
- Raise a glass in their honor at family reunions and gatherings - never forget them.
- pray for peace, tranquility, and acceptance for yourself and whomever else needs it.
- ride again when you are ready - and don't be shamed into not riding because you might feel it disrespectful. As mentioned already - ride in their memory and let your cuz ride with you in spirit.

Peace to you and your family & friends.
Steve