Why'd my husband delete his FB account with me but continue one with his ex?

My husband and I have been married for 6 years through arranged marriage. We have a son (5) and a daughter (2). He was never on Facebook, whereas I have been for some years now. He never seemed inclined and I didn't fuss over it. However, a few months back out of curiosity I searched his name on FB and realised he had opened an account for more than a year. When I asked him, he shrugged off stating he never really used it and had opened one on insistence of his colleagues and to connect with friends from his days abroad. When I asked him why hadn't he added me? He just avoided it saying he never uses it. Nevertheless, I added him and though he seemed reluctant, he eventually accepted it. I checked his account and indeed most people on his friend's list were his colleagues from work and few old friends. He had a picture from his late 20s as his profile picture (he's 40 now). He hadn't filled out any details and he hadn't put a single picture of us or our kids. I was not too happy but I thought he wanted to keep things private and professional and let it be. I am alarmed now because suddenly last week, after having me on his friend's list for four months, he's now deleted his FB account! I searched for him but there's no trace of him (even a friend confirmed this) but now to my surprise, I've come across his another account that is almost 8 years old. The account is set in private mode, I can't see his friend's list but can see some pictures he had posted in public mode 8 years back. He had pictures of his from his late 20s and early 30s, as well as lots of pictures of his niece, a toddler than. On one such picture of his niece, I found a fond comment by a woman. I checked her profile, she is in her late 30s now, lives in another country and is single. When I did my snooping around a bit, I realised, the woman was my husband's ex, the one he loved before he married me. They were in a long distance relationship for five years and had to part ways under pressure from family owing to their religious differences. I checked up further on the woman's profile and realised she doesn't have my husband on her friend's list and her posts were work related. So far, I believe, my husband and his ex are not in touch with each other but I have a nagging feeling he isn't over her yet. Although, they're not on each other's friend's list, through her comments, she's there for everyone to see, whereas I am nowhere around. Ideally, my husband could have deleted that picture with his ex's comments on his profile but he has not. He doesn't seem uncomfortable and it seems, like all his friends and family knew about them and even acknowledged her. Honestly, I had an idea that he was involved with someone in the past but not to the extent I have figured now. As far as we are concerned, we have never shared anything out of ordinary but it has been ok so far. However, his reluctance to accept and acknowledge me and our kids on his social media profile has got me thinking now. I can still deal with his reluctance to post our pictures but I can't fathom his hesitance towards posting pictures of our children, when he could post pictures of his niece. Please help me understand what could be his compulsion or motivation in acting the way he's.

It seems like its a disconnect somewhere. He should not be hiding the fact that he has a FB account from you if you are married. The whole time you were explaining this situation I was thinking to myself is this her husband or her boyfriend. I would ask him why he feels the need to talk to his ex and see what he says.