Feeling very insecure

How would you feel if your husband added a female he use to be close to on Facebook and who his mom claims they went on a few dates before? Well he also messaged her saying stuff how he missed talking to his "best friend" and said he wants to invite her to the baby shower he is throwing for me.... I've NEVER met her before! And besides the fact I'm his wife, I feel like I should be his ONLY best friend not him saying it to another female.... He told me I have nothing to worry about but that isn't the point. I find it inappropriate and it's not like I don't trust him, I really do, I'm a girl and I for sure do NOT trust girls at all, besides the fact I saw her on Facebook and thought she was really pretty and he did "she use to be pretty but she isn't anymore"