Okay so I was playing Skyrim and said to Lydia "We best part ways.", so she left I couldn't find her anywhere! But then during the Imperial mission: Fight For Whightrun. She is chasing the last 3 Stormcloaks. So I see kill the Stormcloaks, then talk to her and say I think "Will you follow me again?" And well obviously she said yes. Then I married her and all was good in the province of Skyrim!