I should have prefaced my post with the fact that I am no vet, but sharing what others have shared with me. It is also much easier to see others situations clearer than your own. I have had a hard time with all of this as well.
It certainly seems that your H has given you plenty of reasons to snoop and sounds like a serial cheater. I am not sure how that changes things. Maybe a vet can chime in.
I Encourage you try pushing yourself with going to a Meetup group or something similar. I can be a shy person as well, so I understand. It would be a good 180 for you. Maybe start with an all women's group. Just commit to just showing up and staying 5-10 minutes and introduce yourself to at least one person. If you are uncomfortable, you can always leave.
Glad you are going to join the gym!! Great start.
Me: 42 H: 40 M: 12 H moved out - 8/2015 I filed - 8/2015