I'm interested in this post mainly because of my boyfriend. He's from another country and came here on a student visa to study cybersecurity and is wanting to upgrade to an H1-b visa after, but with the current political environment it will be extremely difficult for him. Me personally want to marry him after veterinary school (3 more years). I'll "hopefully" be doing a residency and don't really want to do long distance plus I love th guy. Our morals, the way we deal with money, religion, characters, line up beautifully. He treats me wonderfully and is so interested in every aspect of my life. And IMO 3 years appears to be an adequate time to date before marriage. Could be wrong, just basing this on my friends experiences. I'm just hoping my parents will agree with that and will support it in case he doesn't get an H1-b visa.
You may want to consult an immigration lawyer or at least really start looking into it now to start thinking about your options. If your circumstances work out, then a green card marriage is not a big hassle. But you have to be in the right circumstances. It's not as easy as any random US citizen can marry any random foreigner and grant them a greencard. For one thing, depending on when he is graduating in relations to when you will be done with vet school, the timeline can be really tight. You as his sponsor (unless his employer is willing to pitch in) need to have an income that is 125% above poverty level for your household size. Shouldn't be a problem even with paltry internship/residency wages, but you likely wouldn't meet that as a student (or even if you did it would be hard to prove). By the time you need to sponsor him, you need to have already collected evidence and have gotten married already. So if that is the route you might need to go, you really need to know your timeline. If he's on an F-1 visa, does his degree allow for an extension of his OPT?
For my SO, marriage really was the easiest way. Even being a greencard holder myself, it would have been a lot cheaper/easier for my hubby to get his greencard through marriage. We were planning on getting married anyway. The only reason we didn't was because as we were planning, SO brought up a prenup because his parents have a significant amount of real estate that he wanted protected. It's essentially a major part of his retirement plan, so it could potentially really screw him up if things went sour. Not that he would want any of it back in the event of a divorce, but the beginning of our relationship/marriage/home ownership was funded by his savings so his front end investment was huge. I essentially had 0 stakes in the game. I'd already sucked up a lot of his current assets, and he doesn't have the best earning potential as an academic staff scientist, so a divorce could really f*** him over given his circumstances.
At that point, as much as I understood where he was coming from, I said that if he was that risk averse, then a marriage based green card was a really bad idea. His ability to keep his career and stay in the states would be tied to our marriage. And honestly, I think that might f*** him up even more than a nasty divorce without a prenup. And I didn't want either of us to feel stuck in a marriage just for the sake of his immigration status. So we just decided to bite the bullet and hired a lawyer and self-petitioned for a NIW. Worst case scenario we could always get married if it somehow failed. He had a really good chance of getting it, so it was a matter of coughing up $$$, and we could afford it so we did. Once he had his greencard, he was free to leave his postdoc and find a real job. In the end we got his greencard then bought a house and got married without a prenup... and I'm still not sure if asked, if I'd rather have $7k in cash back to have his immigration status depend on our marriage. Thankfully I don't ever have to think about it because it doesn't.
If your SO is okay with packing up and leaving in case of relationship failure, marriage is not a bad way to go. My brother sponsored his wife and it was easy peasy. Being able to check that box on job apps that says you are authorized to work opens sooo many doors. You become much easier to employ. For my hubby, it would have been exponentially harder to procure a job without his greencard past his postdoc position (at least getting an H1b is super easy for that because his field is non-capped).
In your case, trying to procure an H-1b and having marriage as a back up probably makes the most sense as long as the timing works out and you're okay with being geographically restricted for specialization (which may mean you can't match). If he's finishing school well before you are, or you're hoping to hop from vet school to internship to residency in different locations and he's on an H-1b, you'll likely need to prepare for a long distance. And you'll likely need to settle for a real job near his employment if your plan is to then get him a marriage based greencard at some point. It's a lot harder, and would take a good immigration lawyer if you are long distance. A greencard marriage would give you both a lot more freedom in that regard, but does put more stress on your relationship.