It's big only if he has an understanding of what it is he's been missing, so to speak. It's bigger to you, as the author, than it is to the character, if you think about it.
I know you want him to have one of those perfect first times, but I'm going to be fairly direct. I'm from a large urban area, and came of age before HIV, herpes, Hep C, and all those lovely things that make sex a crapshoot nowadays. The worst thing we had to deal with was a bit of clap, and antibiotics along with a bunch of embarrassing phone calls dealt with that nicely. So, we were largely uninhibited when it came to sex.
I have not ever encountered anyone who had two women suck him off as a first time. It sounds like they at least have some clue of what to do, which makes it even less probable. I'm pretty certain that most first times, for a guy, are over far faster than he'd have liked, and are fairly messy, inelegant, downright giggle-worthy affairs. So two women with a clue aren't going to be "playing" with him. They will know with certainty that he's going to blow his load fast, and refractory periods being what they are, even his youthful enthusiasm won't make a second time happen instantly.
And "something large left his body" sounds like he either gave birth or had the bowel movement from the hells. Or possibly he has balls the size of an African elephant. Most men's testicles aren't going to hold enough fluids to give that sensation. We're talking generally a teaspoon or two of fluid, maybe less. Go look at what a teaspoon or two of a liquid looks like. It's not something large at all, in terms of accuracy.