Is it normal to want to suck someones cock?

If you feel comfortable asking your cousin, go ahead and do it. But I would start with watching a gay porn with him first. If he is really turned off by it, you should not pursue it.

If you do do it, make sure to swallow when he cums.

if you guys are already jacking off together then just get up your nerve and reach over.

if you guys aren't at that point then leave it alone.

you're gay
face it
nothing wrong with that

First play with your dick in front of your cousin, if he plays with his in front of you, you can just casually reach out and start stroking his for him. If at this point he sort of just lays back and enjoys the moment, you know you can go one step further and take his dick in your mouth and suck it like you been paid to do so.

I for one will not mind if you want to suck my dick, hell I`ll even suck yours for you too!

I would say as far as your cousin goes I'd skip that. If you really want to take a chance at sucking some cock I'd give it a go, doesn't mean your gay or even "bi" by many definitions. Just means you're open to trying both sides of the coin.

Don't ask your cousin, that's just wrong and you're going to have to face him for the rest of your life.