From a reasonable point of view, since you are a particularly good roommate, you must go. If you can't afford a round-trip ticket, you can call or send a WeChat to explain the situation to the other party and deliver the gift money to the other party by transfer. The reason for this is the following：

First of all, because they are close friends, I think it is very appropriate to be present at such an important event in life as marriage, so at this point, if conditions permit, we should go.

Secondly, because college students are often far apart after graduation, it is often difficult for us to pay high round-trip transportation fees due to the influence of geographical location. Therefore, at this time, I think we can contact each other to explain the situation first. I believe that since we are close classmates, we will understand you. Then, we will attach a gift to show our sincerity and apology.

Finally, express your blessings to each other. I believe that friends can understand each other.

To sum up, everyone should consider their own actual situation when encountering this situation, and it is not recommended to hit the swollen face and fill the fat man. Since we are friends, we should understand each other. I believe that as long as I explain it well, I will definitely get the understanding of my friends, which is conducive to the long-term maintenance of the relationship between the two sides.