Should I follow my BF's friend on social media?

So background info: My boyfriend is in the military and currently out of the country. A few months ago we briefly broke up because I found out that he had been talking to another girl before he left. This girl (as well as all the people who previously worked with him) didn't know that he had a girlfriend. He had not added anyone from his job on Facebook or Instagram. He only let them follow him on twitter where he didn't post much about me. This girl did try to ask about me since she saw I tagged him in posts but he would tell her that I was just a friend. I finally found out about her, we had a rough few months in which we broke up but then got back together.

Fast forward to now and I am getting those uneasy feelings from one of the girls currently in his unit. He's always talked to me about her but a few weeks ago he told me that she broke up with her boyfriend from back home. Now she's been in a lot more of his snapchats and when there are pictures posted of his unit on facebook (the brigade has a page), she's always standing next to him. Recently I realized that her Instagram isn't set to private so I looked at it and saw that she tagged my boyfriend in a picture of the two of them and he commented how much he loved that picture but he never showed it to me. It was for the most part pretty innocent, except for the fact that we've been down this road before. Now on Facebook I noticed that when I've tagged him in things after we got back together, they don't show up on his wall or in his tagged pictures. I've asked him about this and he said that he checked his settings so that everyone can see the pictures that he's tagged in but it didn't make a difference.

I'm just afraid that he's once again keeping me a secret.

I am considering adding the girl on Instagram because I know that she will at least be curious as to who I am and check out my own page and see the recent pictures and posts I've made about my boyfriend. I think this would be a pretty low-key way to test the waters and see if his friends do know about me or not. If it turns out that she did know about me, I'll just seem a little weird for adding her but I don't even know this girl so I don't care what she thinks of me. If it turns out that my boyfriend was keeping me a secret then I'll know that too and I can leave for good.

Should I do it?

Honestly, if you have to do all this, you don't really trust him and he probably isn't trustworthy. Do you really want to bother? You already know what's going on. That's why you're on here posting. That's also why your boyfriend is hiding things about you. Sounds like a crappy boyfriend. Do you really need this girl to confirm it for you??

He cheated, lied and kept you a secret. I think you should ask why you are still with him??????

Stop playing detective and dump this guy.

When people show you who they are, believe them the first time.

I have a tip for you on these types of situations - you dump the guy who can't be faithful to you instead of trying to keep track of his women. Seriously, examine your own life and what you do or don't have going on in it, because you just should not have time for fools who chat up other women to the point that they have to ask about the girlfriend and then get told they don't have one.

He treats you horribly by cheating and you treat yourself horribly by staying. Just dump him already.