I would say to just be honest if you're in it for the long haul. I've been with my gf for 2 years now and she's 5'11 and I met her at 275lbs. I told her about my interests about a month or two into the relationship when we talked about our weird kinks. She didn't really think much of it, but she loves how much she turns me on by just existing. Due to comfort and the fact I'll do anything I can for her, she's around 320lbs now (it's all gone to her belly and ass). One thing I have learned that helps is to find their guilty pleasure snack and just keep it stocked. My gf likes Sam's club croutons with teriyaki sauce from her favorite yakitori place (and thankfully they sell bottles of the sauce) and cheese if we have it, and she'll have a bowl of it like it's cereal. Last night I watched her eat 2 bowls of the croutons, almost half the bottle of teriyaki, and almost all the cheese (and this was a couple hours after she had dinner). While she's not necessarily into this stuff, she loves being pampered and likes when I rub her belly. Also she knows how to get me going by messing with her belly or walking up to me with it out and pushes it against me, and always tells me to make her bigger while we fuck (which she has said she likes to do in the moment cause I love to hear it so much). Sorry for the rambling, I almost never comment/post and thought I'd throw my 1.5 cents in