Girls don't care, they won't think you are gay. Nothing you do with a woman is gay so don't worry about that. Just make sure you are clean and she'll most likely go for it, just be upfront and honest. Good girls are pleasers so if you like it then they like it.
It is a crazy awkward conversation to have. The hardest part is starting it. "So babe, how do you feel about finger blasting my butt". See I couldn't even type that without laughing and feeling weird.
I was hesitant to ask her at first, but when I did she loved the idea. She loves using a vibrating anal/prostate toy to stimulate my prostate while she gives me a blowjob/ She says that I produce more cum like this and she loves a mouthful of cum.
I think it depends a lot on your comfort with communicating sexual desires. If she's out there shopping with you, you might suggest an anal toy. As asked by Herzer above, does she like anal play? In a lot of cases people seem to just jump into something drunkenly. That's generally a bad way to go about it, alcohol or other drugs are not going to help the experience, if it's something you're exploring you don't want to be stumbling, but if you have a drink or two it can help you discuss things. Best to talk and get some input, but if not, you can surreptitiously work a finger towards her back end (very slowly work your way there, don't just jab!). If she responds positively or negatively it can at least help break the ice. My wife seems more comfortable with me using anal toys than asking her to do anything back there, so see what she's comfortable with.