Shift Romance

Last night at the bar, a regular named Alex came in and we ended up getting pretty chummy. We joked around like usual, but by closing time there was an undeniable tension between us. After work, I invited her back to my place for some drinks and it didn't take long before our flirtation turned into more than just fun banter. By the end of the night, we ended up cuddling on the couch with a light kiss, both of us wondering if this was the start of something or just an impromptu hookup. I’m engaged but feel so drawn to Alex. Is it normal for old friends to suddenly have feelings like this? Should I consider breaking things off with my fiancé?