And then I read on here of all these awful guys and the horrors of online dating and I can't help but think whether I should give my marriage another go.
What do you mean, exactly? That you can't be bothered to look for someone else, as it's too much hassle? That a relationships board where people specifically go to discuss their problems or bad experiences gives you a good insight into what most men/dates are like? If that's not what you mean, what do you mean?
Who do you vent to at the end of a stressful working day
Nobody. I go out for a jog, take the dog for a walk, watch something funny on TV, paint a picture, think through whatever it was that bothered me and try to reframe it. If I do mention it to my bf it is usually as a funny story about something ridiculous that happened. If I was so stressed that I couldn't wind down that way, I would try to do something to sort the issue out.
when you look in the mirror and feel shit about yourself?
This isn't a regular occurrence for me, not because I look like Angelina Jolie but because I went through (good) counselling after my exh's affair, read some well written books, listened to podcasts and learned a few tricks. If I do have a negative thought when I see myself in the mirror, I can usually either shake myself out of it and laugh at myself, or (again) reframe it. Focus on the good bits, put my looks in context.
I wouldn't mention it to anyone else - I can't say that I find it reassuring to hear other people politely trying to cheer me up by saying that I look fine. And I don't want my bf in the role of saviour.
Sounds to me like your counselling might be focusing on the wrong thing? Perhaps you need to spend less time talking about him, and more time getting your confidence back. If you change counsellors, do make sure you get one you click with, as that is at least 50% of the effect.