
Haiz... seriously, emotional control is difficult to master especially when peer influence, pride and lust is strong. We all know the right thing to do at the right time logically, but when we are thrown into that situations, emotions BLIND us entirely and the result turn out to be a bunch of rubbish regrets we feel later on.
You wife is pregnant and while you told her the truth, she kept quiet at first while is BECAUSE....
I) Psychologically giving excuse to defend you. She being pregnant cannot satisfy you sexually. You probably seek elsewhere to get some form of kicks.
II) Being honest scores points. You are honest with her, therefore she cannot take advantage of this. If she found out herself, trust me, hell hath no fury by then.
III) Analysizing current situations about the relationship between the both of you. This is the most important consideration - weighing physical or emotional betrayal. In some sense, the latter is more dangerous and fatal than the former.
These 3 points completely conflicts her mind and heart.

***
You only have one option to choose. Love her? Avoid situations where you know you will hurt her. More important, I hope you realise by now avoiding desire is 2nd degree solutions. To prevent future related-similiar crisis, you have to acknowledge that girls will always be around and only yourself can battle your desire because if you land in situations where you cannot avoid - you are alone.
CEASE lying of all form immediately. Censoring of information is no wrong, provided it's reasonable.
Love Seventh Law stated: Lying destroy intimacy.
Renew, rebirth, recover.
P.S: Others may be better than your wife, but she is certainly the most suitable for you.
Cheers