OK, so you do have some renewed trust in him already if you can reassured by him saying that you have nothing to worry about. I didn't think that would have reassured you a couple of months ago. So, good!
It's also very good to discuss these things in a calm manner and "defuse" it that way. I am glad you guys had a good conversation! So, apparently he DID notice the FG with you!! Just trying to imagine being BF in that situation, I think I do understand his fear of acting possessive at this point. He's still unsure of what the R is between the 2 of you and acting possessive might worsen things. Also, towards him, you have always been very clear and strong about what you want and not afraid to set boundaries, so it makes sense for him to believe that you are more than capable of handling FG.
You're in a difficult process pearl! On the one hand you were detached from BF and being independent and strong. It seems to me you have made a big change in that regard to being much more dependent on/affected by his actions right now. Maybe that's why BF is not sure on how to behave?