If there's one thing I've learnt about being in relationships is this. You can be vulnerable and emotionally open with a woman it's not hard. Most of the time either as a guy you choose the wrong woman or you are scared to be open because you don't trust yourself (that's the real issue, lack of trust in yourself in being able to handle your own shit)

Something I did with my girlfriend was tell her this "If I express or say something that is emotional in nature I'm not looking for you to solve it or anything, you're only role is to actively listen that's it understood! I can take care of the rest!"

This let's her know you can handle your own emotions without being a lunatic and you don't expect anything of her when you do share something. Most of the time people have this naive bullshit expection of sharing = you want her to do something about it. That's not the case, set that boundary up before hand and you can share anything (if you want to, I don't recommend sharing everything personally, I've got my own reasons not too)