We're both 20 and have been together for a few months. When we have sex he literally only lasts maybe 2 or 3 seconds. It's not that he's nervous and we talked about it a bit before and I told him not to get upset about it and that it doesn't change how I feel about him. It's not like I'd breakup with him because of this but I'm wondering if it will change on it's own after we've been together longer or if this will always be how it is.
If it isn't a nervousness/stress or confidence thing, which can cause this, he needs to see a doctor. There are treatments for guys who simply can't control their urge to ejaculate, some of which involve decreasing the sensitivity of the penis with special creams.
It won't unless you make a bigger deal about it. I was my ex boyfriend's 7th partner and he told me he always had this problem so he used to just drink a lot before he had sex, never faced the problem head on. I had to talk to him about it quite a few times before he did something to fix it and by the end he was a ton better. I unfortunately kind of hurt his feelings in the process, because I was honest about the fact that I didn't desire having sex with him much because of it (and that he was doing nothing to fix it). I feel bad now about the way I handled it, but he thanks me now for saving his sex life.