Last May I starting talking to someone I met online and for the next 16 months we spoke almost everyday and developed a great friendship although we never met in person. During the summer I couldn't shake a feeling of something being off, he had spoken before about not liking social media and having the privacy setting up high so when I couldn't find nothing felt off but I found someone he talked about regularly and through that found that everything he had told me was lie including his name. He had said to me he was single and had been for while and lived nearby but in truth he was in a long term relationship with a child (who he referred to as his nephew) and lived about 100 miles away. There were a number of reason why we didn't met which oddly never bothered me until the summer.
The level of deception he used is/was on reflection worrying as he stole photos from various people's social media, one extensively as she was referred to as his sister and mother to the nephew. Endless stories were given to me about her along with screenshots of messages from her and other friends and family members which frequently referred to him being single and living the live I thought he lead.
There were a number of other things he did to back up the lies as when I looked back on everything I ended up with a 7 page word document of the lies he told. I had sent this to the Samaritans as dealing with the level of deceit and trying to understand why left me with a number of issues as for 6-7 weeks he had promised an explanation but continued to find reasons not to provide one and I continued to speak to him like normal because a part of me needed to know why and didn't want to do anything that might jeopardise that. A very brief one was given and he insinuated he stayed with his partner because he didn't want to leave his child despite being unhappy. I asked a final time a month ago if an explanation was ever going to be provided but he never read the message.
My question is do I tell his partner as a part of me is overthinking what type of person goes to this level of deceit as to me it feels very concerning and if I was her would I want to know. I'm also aware telling her makes me seem like a scorned woman