Ilya calling himself Shane's boyfriend was actually a very necessary step and not only because it was the first time they'd said it out loud. When Shane tells Ilya his plan for their future, he says, "and maybe, one day, when we're both retired, we can be together, for real" (hopefully I'm remembering that right). Ilya still has to play another season with Boston, so they will only see each other 3-4 times over the next year. They have still had no conversation about what their relationship will look like before Ilya moves to Ottawa. They have not even had a conversation about what their relationship will look like after he moves to Ottawa. They know they will "be together for real" when they are both retired, but what about until then? What will their relationship look like behind the scenes? The title of boyfriend implies a committed, and in their case monogamous, relationship with certain expectations of visits, communication, etc. It means making the drive to the other's city as often as possible. It means openly treating the other person as a priority. It means celebrating holidays and birthdays together. By declaring himself Shane's boyfriend, Ilya is instantaneously making many decisions for their relationship that they hadn't had a chance to discuss yet. He is telling Shane that they aren't going to continue an unlabeled and undefined relationship until things are easier. He knows it will be hard to be in a long distance relationship for a year when they can't visit each other due to their secrecy and their schedules and he wants to do it anyway because anything is worth it if it means he gets to have Shane completely.
Shane has also been yearning for Ilya to be his boyfriend for a long time. The difference is he never let himself want that. The desire terrified him, the implication that Ilya was more to him than sex when he knew they couldn't be together and that he wanted to live a life with a man when he still was trying to convince himself he would some day meet the right woman. He never allowed himself to even for a second imagine Ilya could want the same thing. Now here he is in his parents' cottage, eating dinner with the love of his life and Ilya is the one to call himself Shane's boyfriend first. In a moment where everything feels so unreachable and undefined, Ilya being Shane's boyfriend is something immediate and concrete.
