Why couldn't my dog get up drooling and stiff front leg tongue hanging out to one side?

my 14.5 year old bichon frise was put to sleep as vet said he was in pain on 2nd june 2011 im still beating myself up as if i could have done more on the day before he was put to sleep he ate some food as usual then we went for a walk to the park when he got out of car he was limping came home was fine that night drank some water next day was fine came back from shops had a bit of runny poo by back door then later did another one outside which was still loose and stuck to his behind still wiped him and i gave him treat about 10 mins later he was falling side to side and could not get up his heart beat was quite quick and was drooling front leg was stiff no usual eye movements no sick but tongue was hanging out to one side when i laid him on floor he could not push himself up to get up again i'm soooo sad i can still imagine him trying to get up on my front room floor, even though he was quite old could not get up stairs has catrasis in one eye seemed just old had him checked at vets about 7 months ago did liver test as we said he was drinking alot of water so no diabetes and liver was fine my friend noticed last week he has a bloated stomach he's had bad gingivitis for a while which i have given him dental chews for but don't work . i don't know how one day we were in the park and he was a bit wobbly it was quite hot so i just put that down to him been hot and old so i carried him around then came home and he was fine to the next day and then the above happened after he had treat on the day in question i was looking in his mouth he had broken tooth. I can't get these questions out of my head was it a stroke as he was drooling and stiff leg or was it bloat or a broken tooth which i saw after he had treat on day in question could i have nursed him back i had to take him to vets they said he was in pain i could not stay while they euthanized him as had child with me now i feel bad about that as well gave him big kiss told him i loved him said he was going to see granny in heaven then he wagged his tail i feel i left him when he was my loyal companion what if he was scared not in pain maybe an ear infection.