J.,
The best advice I can give is to be consistent in dealing with behavior issues. Let your son know what the consequences will be and follow through immediately with them if he doesn't comply (time out, removal of a toy, etc). Also be immediate with rewards when he does comply (stickers, hugs, etc). I have also found the when my husband and I use the same approach I mention above and also verbally back each other up ("Mommy told you to give the doll back to your sister") we get better results. Redirecting to preferred activities seems to eventually get results.
When I feel stressed and need to deal with it on the spot, I make sure the kids are safe then I leave the room for a few minutes and take care of me - have a snack, read a couple pages of a book, yell into a pillow, log onto Mamasource. :)
Does your boyfriend know you feel overwhelmed? Sometimes guys aren't in tune to what we are feeling and what we need so we need to spell it out for them.
Hope this helps.