Catching feelings for a long term friend?

I've been hooking up with one of my friends for years. We have always been in different places and doing different things. We dated other people. But every chance I get when we are in same city/country we see each other and have a great time. When we were teenagers he was never emotionally available. Now we have just graduated college and we both went through breakups a few months ago, but we've been in the same city ever since and seeing each other. We go to dinner and have casual sex all the time. He even took me on a boat date. We have a really amazing time together. But ever since we were young, it has only been casual because of the place and timing, but we get along perfectly and know everything about each other. Only thing is, is his lease is up in January and he is moving out west... and we will also be separated during the holidays. But I've realized I want to marry him, and I have a feeling deep down that he is the one. We are still a little young for marriage and need some more growing up to do. But I think I'm in love with him, what do I do? Do I tell him?
Catching feelings for a long term friend?
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