Guy's Behavior

What does a guy mean when he says "I'm comfortable with you"?

So I know the statement is pretty clear to some of you, however, I just have to confirm. Me and this guy decided that we didn't want anything serious (we're just fwb) and we are free to talk to other people. We talk everyday as if we were close friends. But today we were talking about how he hasn't had sex in a while and he practically feels like a virgin because he's so "out of practice". I told him that he should get practice by messing with other girls, and my weird self even said, "Hell, I'll help you find some!". He said, “Don't play with me.” I asked him what was the problem, and he said, “I'll only f*** one person, and that is you. I'm comfortable with you now if you know what I mean. Are you comfortable with me?".
... I didn't know what he meant. I thought we were clear that we didn't want a relationship. So did this mean that I'm going to be his only sexual partner in this time being? Does he want a relationship? Am I not allowed to be in a intimate relationship with anyone else? I really don't know. I didn't want to make him mad by asking what he meant because he's like that. And honestly, I don't mind trying if he wanted a relationship. I just don't want a complicated relationship, and the way we started off is creating that situation. Bottom line, what does he mean?
What does a guy mean when he says "I'm comfortable with you"?
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