Should I take my father back into my life after he abandoned me and my sister a week after my mom died?

When I was 9 and my sister was 5 my mom committed suicide by cutting her wrist in front of me and my sister while my dad was at work. It was a really hard time for me and I still have nightmares about it even though I am 21 now. It was made worse I think by a week later my dad leaving us with my aunt and uncle and leaving to New Zealand to go back to his parents. The only thing he said before he left was that he was sorry and he would be back once he got his head together and that we would leave New Mexico and live in New Zealand. He never came back, he called once a year maybe and we got a card with some money sometimes on christmas. He never called on birthdays or anything. I recently had a baby and he found out about this through a family friend. He calls me and says that he is sorry about leaving us and that he wants to come back into our lives again and meet his granddaughter. My little sister has already forgiven him and has even bought a plane ticket to see him, but I am not sure if I can forgive him. I do not want to bring him into my life and have him leave when things become inconvenient. However, apart of me wants my dad back. Any advice? Or has anyone had a similar situation that can share some wisdom?