You grieving is not wrong or bad or an overreaction, anyone who tells you that is just flat out wrong. Try your best to to grant yourself time to be sad, even when you feel like you don’t deserve to. Trying to repress/suppress such strong emotion is one of the strongest poisons you can inflict on yourself. With enough time, you will absolutely find acceptance and solace, and you will have sweet memories of the times you had together for the rest of your life.