What does he mean by "let's cool it for a while and be friends"?

I've been dating this guy for a few months everything was all nice and rosy as usual. We were basically messing around at first not taking it seriously. We said we were gonna take it slow and we would always have discussion about it. Then all of a sudden he starts being distant, stops calling like he used to and started acting differently and then would ask me questions about making our relationship official and being committed. That was obviously confusing me because I didn't know what he was or I was doing anymore. We then chatted and he said he thinks we are moving fast and we should slow down because he is stressing and we both have different things to concentrate on and I said OK but then he calls me every other day and asks me if I'm still gonna come see him and I did. When we met he was so cold towards me and wasn't chatting and it was just pointless and he goes to me so is it ok for us to be friends because you have different plans to mine. So let it be break and then we can start concentrating on each other afterwards. So we are on a break what does that mean?
What does he mean by "let's cool it for a while and be friends"?
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