HELP GERBIL CRISIS!!!?

My gerbil Arnould is skin and bones, i can feal almost every bone in his body. Im so sad and upset im crying, i no it sounds rediculious but im so afraid im going to lose him very soon. His eyes are sealed shut and when he walks he wobles, its so sadning watching walk...... I have always provided him and his best friend Rocky with fresh food and water. Can vets see small animals? I have had him for like 2 or 3 years and i no they only live for about five years. His underbelly is coved in feces. My my cousin said if its just "That Time" then for my to provide him with fresh fruits. My mom said that if it is time that he has had a very nice great life, if it is truly that time than i want it to be the most comfortable, relaxing enviorment possible for him. Please if you have any info that would be useful, please do, i want him to have his last few hours the best he has ever had. Thank you for helping, God Bless.