Proposal from long term boyfriend during sex?

my boyfriend and I have been together for a little over two years now. we truly to love each other and would do anything for each other. I have brought up getting married before, just as a thought, nothing serious because we are still young. whenever I do bring it up, he gets upset with me and yells at me and then refuses to talk about anything that has to do with marriage. but, the other night while we were having sex, he asked me to marry him. when I asked if he was being serious he said yes. after we finished I wanted to talk about what he had said but he brushed it off like it was nothing. what does this mean? what might be going through his head? I'm so confused and I could really use input/advice. thanks!

Proposal from long term boyfriend during sex?
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