I used to really worry about that too; everytime I dated someone, no matter how brief, I would get stressed and obsess over them and would spend my time worrying and not feeling like I was myself. I used to worry about why they liked me?, whether they would cheat on me?, was I boring?, did I make a bad impression?, where they regretting it?.... etc. etc.... With all that worrying, there simply wasn't time to do my own thing and I felt I had lost who I was because I knew I was prepared to sacrifice and hide so much of me to make it work.
It's different when you are with someone you generally like to be around, and who you know enjoys your company. A lot of the stress goes, and you find yourself often preferring to be with them than on your own. Once you want to be with someone, it's not a sacrifice really.
The idea of spending an evening watching bad TV programs with one person would have made me shudder a few years ago, but these days it's the norm, and I enjoy it.