Job problems

My ADD husband told me the other day that he will probably be laid off in the next few weeks and I am trying not to completely lose it.  He is 55, diagnosed about 5 years ago (though I was sure for much longer) and takes medication.  We've been married 28 years and have 3 kids and his job situation was surprisingly stable for most of that time.  He had one job for 10 years and another for 15 years--they weren't very challenging but were solid, with benefits, etc.  Five years ago he was laid off--I never really got the real reason, but he was out of work for 3+ years and it nearly killed our marriage, our family and me.  I am trying to stay calm--I have a good job and can support us, but I have one child in college and two more in high school and I'm not sure our relationship can survive this.  It was so incredibly stressful when he was out of work and now he is older, will have another "failure" to contend with and the pressure of knowing that our two younger kids will not be able to have choices in going to college because of him.  I don't think I can take going through that again.  These years of dealing with him have just sucked all the life out of me and I really don't love him enough to suffer through this again.  I hate to think that I would end this marriage because of him losing his job, but it could be the last straw.  Even since he started working about a year and a half ago, life has not been much better because trying to keep up at work takes everything out of him and now I am back to doing everything on top of working full time and making sure my kids are OK.  He is good about taking his medication, but that is all he does.  He has not followed through with counseling and though we took Melissa's course last year, he isn't interested in using anything we learned.  I have really tried to be understanding and not pressured him at all so that he can do what he needs to do at work--but apparently that may not be working either.  Sorry to go on and on, but I really don't know what to do.  Any advice will be appreciated.