I have a superb memory and oh boy did he mess with me, big time. Gaslighting is ugly stuff. Mine cheated, a lot, and he often used this technique because he was a terrible liar, so he was often very seriously trying to convince me I was wrong or forgetting. "This bracelet? I've had it for months. In fact I stopped wearing it over the summer because you made fun of it saying it was stupid. I had bought it because it reminded me of you" ... .brand new gift from a lover. Yep.
Not only that but as some others said previously, there was a lot of "You always think this" going on from him, which would drive me up the wall (because of "always" and his magical powers to know what I think) however at the same time he would correct and nitpick my word usage. Full blown hypocrite.
He challenges every thing I say. I usually retort with "Am I a liar?" because I'm a smart mouth that argues back. I am also annoyingly truthful and honest

(Aspergers) and if I do not know about something I will begin by making that very clear (I'll use phrases like "I think but I'm not certain" or more often I will directly say "I'm not sure" or "I don't know anything about that" however if he would ask a question and I would begin to answer he would constantly question me, or give an alternate version, and add that he thinks I'm wrong. When I call him out on it he has stated, repeatedly, that he thinks he does it because he "wants me to be wrong just once". He takes it as some kind of personal insult, me being right. Good stuff.
It even went on with little things. He still to this day looses everything, keys, his hat, wallet, sunglasses, etc. Then he'd have a temper tantrum "I PUT IT RIGHT HERE! YOU ARE AWAYS MOVING MY STUFF!" ... .uh, no... .but now that I understand I do wish I had done it at least once for the fun of it, since I was ALWAYS getting blamed *

*.
He consistently would ask me questions about my plans over and over and then seem genuinely surprised or confused when they would finally happen. As if he didn't know about it well in advance and often in detail.
I used to think he was doing it intentionally to make me insane (I have an issue where I deeply dislike repeating myself, so I thought it was a mind game of his). Then he'd go right into stonewalling (ignoring) me after hours of this twisted reality.
17 years of it. I don't know how I haven't lost my head. They should give out medals for enduring this hoopla.