How do I be in a relationship with someone who has a platonic relationship with a female?

I have been in a relationship with a man for a year. It was a girl he spent 4 weeks and it almost was a relationship but he turned it down and they kept it at a platonic relationship and when I met him I wanted it to end because I thought it was more and they way they complimented each other and talked to each other made me jealous. He stopped talked to her but I felt like it put a hole in our relationship which it did.
How do I be in a relationship with someone who has a platonic relationship with a female?
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