One of the main reasons for a legal separation is to protect your interests until you either divorce or get back together. Laws differ from state to state (I am in Chicago, IL) so check with your locale to see a lawyer there who can talk with you and get familiar with the specific terms of your particular legal separation. When you are separated you are still legally married to your spouse, so having a sexual relationship with someone else is likely considered adultery. As to whether it is okay to date once you have separated, that is something you need to discuss with your attorney because many strategies come into play to keep and protect your interests.
Get a lawyer and talk things over.
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