IT ALL CUMS DOWN TO THIS
Pretty much every porn session ends in a climax, here's some advice we can give you:
It's not a race, be a gentleman and make sure you don't come first. This is respectful to your bud and shows that you put their pleasure first. It's also helpful as you might feel slightly uncomfortable with the whole idea of a (bi)sexual relations with a guy and staying aroused is by far the best motivation to keep at it.
You're not a pornstar. While you might be fantasizing about it, it's probably not the best idea for your first time to end with them coming down your throat or giving you a glamorous facial. If you see your partner is nearing orgasm while you're sucking their cock, it's OK to stop and jerk them off onto their stomach. It's not the last time you're doing this, save some of the exciting stuff for later!
Get familiar with cum. Play with it, maybe put it on your cock and use it as lube, enjoy the smell and the texture. Hell, if you're curious about the taste, scoop some of it up and give it a try, maybe even lick it right off your bud. A few minutes of gentle attention while they're recovering from orgasm expresses your enjoyment of the entire experience.