There's a great deal of love and comfort in sex that's quite different from the way it's sensationalised and trivialised in the movies. It's also an affirmation of life -- and that's something we all need when we lose a loved one.
It is part of life you don't have to feel bad about it. It might even help you feel better because you will have your boy/ girlfriend closer to you. Being intimate is not going to make the pain go away but doing it will not make you grieving go away either. Sorry for ur loss.