<human>: Can you give me the gist of the text in a nutshell?

I've had issues with anxiety for as long as I can remember. It has become much more manageable in the past year and a half, in that I can recognize when I am feeling that way and (at least attempt to) look at it objectively/rationally.

Backstory. I live about 4 hours away from my boyfriend. See him a lot; as often as is possible. I will also be moving to the city he lives in (not living together) to go to the university there, at the end of this month. We haven't been together but about 4 months or so, but I feel I have connected with him in ways I never have with anyone before. 

Yesterday, he calls me, and we chat for a bit, then he brings up a conversation we had a couple weeks prior, in which we talked about an open relationship, but decided that we wanted to remain monogamous. He said his feelings had changed and he wanted to see what I thought about having one. 

My first thought was "No, No, No." The idea of him doing things with other people is very anxiety inducing. He said that it wouldn't possibly change his feelings toward me, and it would just be until I moved there, in a month.
<bot>: Boyfriend of 3-4 months asked for an open relationship, makes me anxious, but I'm trying to see the good in it.