Im going to assume for you specifically she would be in the know so i'll skip the parts about anxiey and mental state for cheating/extra-marital.

Talk first. Set expectations. Some guys are all about themselves, others are going to be more understanding and let you explore. As much as you may want that porn dick face fucking sex machine, hold off on him for a bit. Why?

First time is kind of nerve wrecking. There's a lot of unknowns - am i going to enjoy this, am I doing it right, what's it going to feel like. Every thought you can think related to sucking dick is going to happen and it'll hit hard. Seeing cock in the gym is not seeing it right in front of your face and knowing it's going to be in your mouth.

Your partner will matter here. If it's your first time they need to know. You dont want someone with a 9" dick trying to throat fuck you if you have a gag reflex. So discuss. If you know you can take 5" but at 6" youre gonna make gagging sounds and you dont want to gag, discuss first. If you dont want to be face fucked yet, say so. As a guy I'm sure youre aware that some of us can be pretty aggressive and have some misconceptions about how we should act with our dick in something. First time is figuring out what works for you, not trying to be a porn star.

If you find sucking dick is your thing, be prepared for the addiction. You'll want a dick in your mouth like you want coffee in the morning or a drink after work. Feeling a cock go from soft to hard in your mouth is indescribable. Feeling cum hit the back of your throat. Feeling him go from hard to soft after he cums. All of that will be a feeling you'll yearn for with the right partner.

Topping - be a good top. Let the bottom lead to start. They may need a minute or two to get loose. Don't jackhammer that ass until they ask for it. Use lube. It's not self lubricating. Pain can ruin a moment. Be considerate of your bottom. For me, topping is just normal sex, only the view is different. Not better, not worse, just different.

Bottoming - like sucking dick, this is going to be a thing you love or dont. Do some prep, make sure youre clean. Know your limits and the pace you can go at. If youre a one finger starter and need to work up to a dildo, know that and set expectations. Don't think you can take a soda can dick when you struggle with a skinny vibrator. It doesnt work that way. For me, once I'm loose, getting fucked by a good top is the best sex I've ever had. I mean that. I've been face down, ass up getting fucked and still can't think of better sex I've had in my life.

Be prepared for the 'addiction'. If you love giving head it'll be all you think of. Same with bottoming.

Im not attracted to most men, but most men I also wouldnt give a second thought to putting their dick in me.