rajp,
You are in a tricky situation. On the one hand your wife has confirmed that she has had sexual relations before marriage, and on the other you have difficulty accepting this fact and the present situation.
Firstly, you are making a distinction between sexual intercourse and oral sex. Either way, it is sex. So, dont console yourself that your wife was a virgin before she married you. Physically, may be, but definitely not mentally. Even physically, having oral sex without fingering the vagina is difficult.
Does your wife come from an affluent family? Does she have the financial resources to go out on dates etc? Are you well employed and financially secure?
Marriage is a bond based n trust and if that trust is broken, it is difficult for a marriage to survive. Are you absolutely sure that she is dating now behind your back? Since she has told you the truth of her sexual encounters before marriage, that must be playing on your mind, and you could be doubting her.
Look for signs of infedility. Is she neglecting the home? Does she dress up more fancily now? Is she spending more time in front of the mirror? Is she continously on the phone? Does she abruptly stop her conversation when you enter the room? You can tell, if a woman has had sex. Is her face flushed? Is she quiet?
These are all forms of policing. Not healthy for a marriage to survive. Find out about your self. Are you giving sufficient attention to her needs? Are you spending time with her in bed and out of it? Improve your techniques of making love. Women will not stray from home, if they are kept happy, especially in bed.
Finally, do not presume that having a child, at this stage will keep her confined to the home. It may create more problems for you in the future. You will always have doubts, whether the child is yours or not? Besides if you ever think of divorce (if things get worse, and she wants out ), a child will complicate matters further.
If there is an elder in the family, whom you can confide in, seek his/her help.