Is my husband hung over his ex date or soemthing?

I am married to my husband for 7 months now yesterday i saw him chatting with this girl (he meet her on shaadi.com which is indian matrimonial website) whom he dated 2 yrs ago i asked him who is she he said my friend but i knew she is not cuz i have read their emails and he had her pictures when she came to visit him then after 2 hrs i asked him did you dated her he was speechless and he said he jus froze and later on he is telling me it's complicated to explain which doesn't make sense cuz it's yes or no question why did he lied anyway in first place and whats so complicated abt her i dont understand