Doubts about Karma and/or Rebirth

I have been a staunch follower of the Buddha's words for the past 1.5 years. I do believe in the Buddha in so far as the Denial of God, Creationism, Destiny is concerned but considering the events in my life and what I see around, I am now absolutely sure that there is no Karma nor Rebirth. In my own life experience, I was married about an year back, arranged by my family according to the traditions. Obviously I did not know the Girl before marriage nor had any sexual relations with her. It so followed that after marriage following a few days of sex with me she went ahead and had sex with her boyfriend (her friend close to her before marriage). What followed was - She obviously found him to be more suitable for her sexual desires and immediately after that she started mentally irritating me and abuse followed. She did other stuff (like creating fissures in family) and ultimately left me after a few months. Now she is extremely happy and posting happy messages and photos in social networking and abusing me happily. The marriage laws in my country are pro female and I cannot do absolutely anything. But the fact of the matter is that she is extremely happy (both sexually and otherwise) while I feel cheated and wronged. Further I do see in my country in India due to a hierarchical Caste system, extremely poor people made to clean others toilets etc and pick trash due to their birth. I just spoke to an old man (about 65 years old) who told me (while crying) that he has been doing this job (cleaning toilets and picking trash) for 45 years and he is not allowed to do any other work except this and there is nobody to help him because the traditions in the country are like that. I would like to ask you for those who believe in Karma: Where is Karma acting?