4 and a half years is a long time. I am conserned that this situation may betray that you two have very different approaches to money in relationships and joint assets.

When my now husband and I were ~4 years in to dating, we went to his close friend's wedding and decided to gift them $500. We were still in/just out of school, so it was a lot of money. We talked about our comfort levels with that contribution, but the discussion always assumed we would split it 50/50. So I lan more towards your boyfriends way of thinking.

The thing is, my husband and I have a joint account apprach to finances. We both still maintain individual accounts, but our paychecks get deposited into a joint account and we budget an "allowence" from that for each of is. We have no "your money" or "my money." and while we only set this up AFTER marriage, that financial philosophy did impact how we approached financial decisions before marriage. Like major gift giving.

The thing is, we split 50/50 when we earned similar incomes. If you two rearm about the same, according to the "our money" philosophy splitting it 50/50 is fair. If your boyfriend is making 20k+ more than you or something, he should cover the whole cost, because it's all "our money" anyway.

I rambled. But you two might need to have a sit down about your individual expectations for your financial future together.