You guys need to have a talk. A good marriage is based on love, trust, & respect.
Silly childish behavior on his part. Sit him down and ask him what the heck is going on! Tell him that this all may be innocent and ego based but how would he like it if you did this. Maybe do it one time and show him the response from some male.
Unless he sees and realizes how this is hurting you by him feeling the hurt himself it may continue to the next level.
You really need to address him about this seriously. Me and my husband have been through many ups and down but we always got through it.. and not because I got over it and not because I made him stop doing whatever it was but because we talked about it. Tell him either stop hurting you or leave and if he does neither than you leave (I dont care what it is if he has to lie or hide it then its not okay).. the important thing is you move forward in your relationship or end it. Just dont stay stuck. You can work through it because people make mistakes dont let anyone tell you your gonna het through life without being disappointed in people..you'll never have anybody then.
Unfortunately you accepted this a first, second and now a third time indirectly. If it was truly a deal breaker for you then you should have ended things with him after the first incidence.
This is "him" and what he does. It's apparent he sees nothing wrong with this if is continuing to do this. If you stay with him this will be something you will have to accept. I am not saying you have to be happy and over the moon about this, but this is something he will not change. It's unfortunate you have to deal with this while 8 months pregnant.
I know I wouldn't like it, however, I would of broken things off the first time I found out about what he was doing. Unfortunately you kept going back.
Two options: Stay and put up with this or leave.
Haha accept it and get over it? Not me girl! I mean dont get me wrong ive had to forgive and forget aome things but ive always put a stop to ANYTHING that mad me uncomfortable when it came to "other girls" my husband (2year ago, fiance at the time) was doing the same thing but on his fb which I found the password too and decided to be nosey.. OH HELL NO! talking to other girl about how gorgeous they are anf sending his number out.. I woundt put up with it... just dont let anyone tell you your in the wrong when hes the one being sneaky..