<human>: Give me a shortened version of the text

So a while ago, I [21] started going out on a few casual dates, and ended up meeting a few great people. Eventually though I started clicking very well with one of the people, and we started to see each other exclusively. 

Today one of the people I had gone on a few dates with (4 times, slept together once) sent me at ext saying he wanted to meet up again. I told this to who I am seeing right now, and he is fine with me meeting up with the other guy in person to let him know I am seeing someone now. It's been about a month since me and the guy who I am not dating had actually met up in person, and we've exchanged a handful of texts since then.  Me and the guy who I am exclusive with have only been exclusive for about half a month, so everything is still very new.

So the issue I am having is I am terrible at doing this, and I have no idea how to say that I am seeing someone now without seeming like a total prick. Any advice on what I could do or say?
<bot>: I am in a new relationship, and need to tell someone who I was on more than a couple dates I am not open to dating anymore in person without sounds like a total prick.