I want something serious, how can I tell him?

The guy I am seeing and I had agreed to a non committed relationship and kept it that way for a year.
He had other girlfriends and that wad fine with me, I had my stands too.
But recently I felt like stopping seeing other guys and I have stopped in January.
I feel more for him and I'd really want to be his only girl and have a committed relationship.
Best way to tell him?
I want something serious, how can I tell him?
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