You're a baptized JW (like it or not). He's a "worldly unbeliever". You will be "unevenly yoked". (WT jargon). Your Elder father will lose his position if he attends a wedding where a JW (you) becomes "unevenly yoked" to a "worldly unbeliever".
There it is. That's the way it is.
You and he should head for Vegas or the Caribbean and just get hooked and come home all smiles. Once you are married, it is "Holy Matrimony" and "what God has yoked......let no man....."etc. Until the "I DOs" are all done, you'll be harassed for dating a worldly guy. If they are aggressive they (the Eldubs) will "mark you" and may try to twist it to DF you (not likely, but possible) for "brazen conduct" when you refuse to call off the engagement and wedding.