What is the difference between the two cases?

You said me the difference. I think you know well than I

There isn't really much of a difference

The actual ejaculation itself is going to be the same whether you masturbate or have intercourse. Other aspects though may be different.

Masturbation is basically stimulation of the penis and genitals manually to reach climax and ejaculate; sex with someone else uses the mouth or vagina generally to do that stimulation. Same end result. So physiologically they are the same for a male. In reality they are different in intensity -- when your penis is in a vagina or mouth the sensations are totally different than just using your own hand. So you get more turned on. Plus you have the rest of that warm body to play with, which you don't going solo. Solo sex is great if you go slow and easy and relish it as you make love to your own body but intercourse will always be more intense and more fun, just natural for that to be. Like most married men I do both, the wife is not always available so I turn to solo sex for release and certainly can enjoy it but intercourse is much more intense, and my climaxes are much much more intense during intercourse. I may even ejaculate repeatedly and climax for a minute or two until totally spent and exhausted, compared to a few seconds with solo activity. So while they are the same physiologically the outside stimulation (another person) makes a big difference. Try doing it regularly without porn, by the way, and just focus on your own body. Go slow and easy and enjoy yourself and see if that gives you some more intensity. And you ejaculate semen,, sperm are only a tiny component of the semen.

Having sex with a partner is much more enjoyable than going solo, psychologically and physically.