Pandora's Aquarium: Is being insecure normal? - Pandora's Aquarium

Ok, I know I've been complaining and complaining but here's more! After several arguments with my husband of almost 18 years about his time he spends on Instagram I feel another argument coming on. A couple weeks ago we had a big argument over IG again, he's on it all the time, it's like his other life that I know NOTHING about. I've talked to my therapist as well as him about how I feel but I can't seem to get my point across. What am I doing wrong? What am I saying wrong or what am I not saying? The last argument went like most, I tell him that it feels like he's hiding something from me, when I walk into the room he puts his phone down right away (usually face down so I can't see what's on the screen). He spends so much time on IG that its like he doesn't want to spend time with me or the kids, he does blame me, he says he's not going to sit around staring at four walls so he's going to get on IG. I've told him that we can do things but I'm not willing to do them if he's gonna be on his phone the entire time, I think that's fair but I guess in his eyes it's not. The day of our last argument I told him that his Instagram life is a part of him that I don't know and I'm very insecure thinking there's someone else because of the secrecy that he's showing. I explained it all to him, things changed for 1 day, that night he actually showed me some pictures people had posted. Ya that only lasted that 1 day, I've never seen his acct again after that. Am I just crazy and insecure or do I have a valid claim to think something's up? I've told him time and time again how I feel but nothing changes. I feel like our marriage is suffering and that IG comes 1st before anything else in his life. I can't go on living like this anymore, I always feel like there's someone else and it's never been like this until he found IG. I can't deal, I feel like I'm going to explode and everyone will hear it when it happens (kinda like a nuclear explosion). I'm feel bad for myself with lots of self pity and I've never had to feel like this before. I never ever felt sorry for myself before, I hate it. I feel like I'm not good enough any longer and I feel unwanted and alone. Today, he's not talking to me much, he must know the axe is about to fall.
Is anyone else going thru anything like this?