The worst for me was also the most recent, just last year.
I'd just lost my dad, left my relationship and moved to a new city (posted about this before so won't repeat here). Said 'friend' was the only person I knew here and moving to the locality I'm in was her idea. It's often said that when you move somewhere new knowing just one person can be enough to get you settled in. Unfortunately for me not this one.
Despite knowing my situation and what I'd left she went out of her way to take advantage of me materially (really don't want to go into detail). She lied about so many things, and when each was discovered she would just shrug it off and tell more. Despite being a bit broke myself I did my best to help her when she said she had no income. This was also a lie, she'd been working. I only wanted to be a good friend and have someone to talk to from time to time. I think I did my best, I phoned and emailed her when she was having a tough time such as problems with friends (ha!), her Ex, a bad job interview etc. and always offered to make time to meet. For a long time she was the only person I knew here and looking back she was clearly very aware of this.
She was the first person I came clean to about my last relationship. What a mistake that was. Many will say that the loneliness is one of the worst things. Well she never came near. Despite living only a two or three minute walk away she was always too busy, despite only working part-time (and sometimes not for days or even weeks at a stretch) and her ds being in school. Many times I changed my arrangements, took time off work to meet for a coffee and she would send me a text a few minutes before to cancel. Sometimes she didn't even let me know and I would just be left waiting.
Of the tiny number of people I've told (friends and professionals) she is the only one who tried to persuade me to go back to my abusive XP (this on the only occasion she came to see me, several months after I moved). I don't think this is because she thought it would be best for me but because she just couldn't be bothered.
The 'friend' moved to a different part of the city at the end of last year and we didn't stay in contact. This was her choice, she sent me a text saying she didn't 'get anything out of it'. In fact she almost always tried to communicate by text and email, despite being so near by. My therapist has described it as 'cowardly'.
I still feel very exposed about the personal things I've told her. I was at a real low point (I've previously described last year as the worst of my life so far) and certainly somewhat all over the place emotionally. Most of all I can't believe I was just so stupid to be so taken in.