Lettie, girl......just be patient. Think of what you would want from him, or what you used to want from him when you were feeling insecure. He will get there......I am sure you two have endured much rougher times. You knw we all have our less than favorable moments in relationships.......and that is why we get married.....marriage helps carry us through the rough spots.
Also, you might want to reassure him the he is not alone.....many men and women feel insecure when their spouse/partner make significant changes in their lives. My DH was kind of nervous when I went back to school, and raised some innocent, but jealous questions about some of the dudes that were part of my study groups. I think they question why we felt the need to make a change, even though they know it is a positive change for us and our relationships. I think they really want to beable to make us happy all the time..........but what they don[t take the time to think about is that we, as women, eveolve over time. Your kids are growing, and you are now finding time to care for yourself, and in time, he will feel more secure about it all.
Now, this part you may not like, as your BFF is a dude........but I can tell you that if my DH's BFF was a woman, I woud NOT be ok with that. I might try for a while to be ok with it....but I woudn't be. Maybe DH is just realizing for himself that he is not ok with it. Maybe he has tried to be the bigger person, but is faling miserably. I don't know, it is just my 2 cednts, but you might want to think about scaling back time spent with BFF. But, really, Lettie....you are the one that knows best. Follow your instincts, and be honest with yourself and DH. And tell him he is a dumba$$ for not taking the extra "attention," in stride and with a smile
Time will show him your faithfulness and committment to him. Sometimes, even the strongest of us do weak things and act stupid as EVER. And, Lettie.......you don't have to take $hit from anyone......no matter how many kids you have......you are a strong woman, you can take care of yourself and your kids.....and don't let him forget that. You are going to have to demand his respect on this, and be patient while he adjusts