I think you've confused your dad not loving you and your digestive issue as related, but they are separate. Or maybe your feelings about your dad contributed to your tying yourself in knots that made the digestive issue worse.

I feel my dad did not really love me, but I forgive him because he was mentally ill and he died when I was 12.

My son has IBS-D and controls it with the Fodmap diet. Have you looked into that? Plus, he has a loving girlfriend who shops and cooks with him, even though he has to adhere to this very strict limited diet.