I think it is very hard to ever trust someone again after they have deliberately lied to you about something that you feel is important, whether it involves another woman or not. If someone loves you, they should be honest with you. Even if it causes a big argument at the time it is better than weeks of suspicion, snooping and ultimately the truth coming out anyway. Some people are naturally suspicious, or have had a bad experience which has turned them suspicious, and true love means helping them through it, not using it as an excuse to keep secrets.
Hope you can manage to work this out though, whichever way suits you best x