This has happened to me as well lots of times. Losing myself in others, taking on their personality, values, likes, dislikes. Especially when spending a lot of time with someone. The thing is that it doesn't happen on a conscious level, you feel like everything is fine, you think you actually like x thing, just to later realise that all this wasn't you and it leaves you confused, but you cannot control it and the next time you are with someone you lose yourself again.

You could be a highly sensitive person or as some call it, an empath, who picks up other peoples feelings and basically their whole personality sometimes, unconsciously, like a sponge. There are a lot of articles on this, though science is still not clear about how this works. But there are many people who experience similar stuff, and many resources online. If this resonates with you, there are also various things you could do, like mindfulness, grounding practices, body awareness-type meditations or exercises, where you connect to yourself to how you feel in your body so it will be easier for you not to drift away into other people's "worlds".
Hope this made sense, and I'm here if you'd like to talk.