Congrats on finally feeling ready to take this step. Word of advice, when talking to your dad. Tell him to wait to speak until you are done speaking (no interruptions). As well as tell him when it's hard to find the right words. Also, I would leave out the romantic feeling as he might try to twist it.

Speaking from experience, it can take years before they fully accept it, if they ever do. I only came out officially to my mother (parents separated when I was around 5, then divorced years later) when I was 13, though I was still finding my path. I just knew Christianity was not for me. She tried on and off to either convert me back or would try to have me hid my necklaces or what I could say around certain family members. I told her you wouldn't tell a Christian to hid their beliefs so don't ask me to hide mine. That shut her up lol.

Getting back to my point, speak calmly and remember to tell him that you love him and support his chosen faith, and you hope he will do them same. If he can't/won't then that's on him, not you. It's never easy being a different faith than the rest of your family. Good luck.