Overwhelming Sadness

Does anyone else randomly feel sad? Like mega sad. Today I have been on the verge of tears all day. I could feel the sadness resting on my chest. It's this weird feeling. Like you have a boulder sitting on your chest. Just when I think I am getting stronger, one thought turns it all around. 

My biological father and I don't have the best relationship. He never talks to me anymore, I tried to call him on his birthday, and he totally ignored me and never even called back. I sent him a text for Father's Day, and he responded with a short "thanks". My grandma passed away at the end of March and he didn't send a card or flowers or even call me. I don't understand why he is like this towards me. He dotes on my 2 half-brothers. It's like he totally forgot that he had a child from his first marriage. I wish I knew what I did wrong.

This afternoon I was ready to just throw in the towel with it. I felt like I was finally done getting my heart broken over and over. Then I saw my brothers at the gas station, and I wondered if they would tell dad that they saw me. If they did, would he even care. Why do I keep trying when I always get the same result with him? 

There have been times we have had really great conversations and he tells me that he would like to spend more time with me. Then after we get off the phone, he must completely forget about what we just talked about because I once again get the cold shoulder. It's frustrating and tiring.