I am so sorry that he's still out at night...it's hard to determine if he's out w/his buddies or w/OW. We can't assume anything, but can you smell alcohol on him or his clothes? Any other strange odors on the clothes, i.e., perfume? Does he have difficulty looking you in the eye when he sees you or acts guilty around you?
Many of them are cowards and won't leave on their own, but they don't have an issue pushing our buttons to make us angry enough that we put them out. Maybe he is trying to push your buttons and bait you into an argument.
Please take some time and make a list of questions that you want to ask a lawyer. It does not hurt to find out what your options are. If you aren't ready to file, don't allow the lawyer to push you into doing so.
I wouldn't recommend bringing a third party into the mix right now. The thing is, if you go out and start dating and if your h is doing it, he will think it is okay to continue doing what he is doing if there is an OW in the picture. Best to wait until the separation/divorce papers are filed and only then, you are sure you want to go through w/a divorce. I know you are lonely, but you can always have several friends get together and go out as a group.
Yes, this is your safe place to come vent and ponder things and hopefully doing so will help you clear your head.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
