Be patient and supportive .. He is grieving for someone he cared about .. He may have said he had "forgotten" her, but it's clear he hasn't. He probably said that because he feels guilt for feeling the way he does. He shouldn't . She was someone he loved at least at one time in his life ...they obviously parted as friends. And because she had passed away he should grieve. It's normal to grieve for a friend. Even though he has moved on to a new relationship does not remove the fact that he cared for her and the loss hurts .. Also normal. It does not necessarily mean it interferes with his feelings about you. Don't make this to be something that it's not .. love him, console him. That's what you do for people you love.
After reading your other post I now get the feeling this ex died while they were still in a relationship and he contacted you and you starting dating after the fact. If THAT is the case ... he's totally lying to you about "forgetting her" .. clearly he is grieving her. I can only guess that his contact with you was based out of desperation because he felt so lost after her death. Why he would jump into a serious relationship so shortly after losing a love partner is beyond my comprehension. That is clearly unfair to you. There is no way in the world that he is emotionally stable after going through all of that AND then jump into a new relationship. He needs to grieve .. he needs to heal..before he even has anything to offer a new partner.
