My Bf Cant Stop Mentioning His Exgirlfriend !!

me and my boyfriend have been together for 8 months..i know its not that long but it is the longest and most serious relationship i have been in. me and him have been through a lot. we met in school and at the time he did have a girlfriend. i didnt want to fall for him because i respected the fact that he had somebody but we still talked constantly on the phone and i fell in love. him and his girlfriend at the time had many problems and i was always there for him when he needed to vent out his problems. i tried to give him advice to make their relationship work because even though i loved him i still respected the fact that he had feelings for her. it turned out that when he finally broke it off with her, i was already getting close to someone else!! me and him stopped talking for months because of that. then i had to move far away(overseas) and i had to start a whole new life single. im not sure what made me do it but i called him one day and we began talking again. i realized that i missed his company and that he was someone i definitely didnt want to lose. we decided to have a long distance relationship...give it a try and see where things went. but just when we were finally getting serious his exgirlfriend called him and wanted him back. he called me on the phone and tried to explain to me that even though he really did have strong feelings for me, he still had feelings for her. that was the last conversation we had for 4 months. i had to find out from a friend that he had gotten back with her. he called me after 4 months of hearing nothing from him and apologized. mabey i shouldnt of forgave him but i did. he was still with her and she didnt want him talking to me. but he went behind her back and did anyways. they eventually ended up breaking up again and he wanted me back. at first i wasnt sure if he was going to hurt me again but i said id give it a try. we went through 6 months of a long distance relationship until i moved back to my hometown where i am now. i cant complain about our relationship because we are great together. the only thing that bothers me is that he constantly refers to her. like when he sees something that reminds him of her he will go "that reminds me of my ex....blablabla" she did a lot of damage to him and i feel like i pay for it. she would hurt him emotionally and he went through 3 years of that. i constantly try to remind him that i would never do that to him but he seems to have this fear that it will happen again. i confronted him about what it was that was bothering me and all he has to say about it is that i dont know what its like to have a relationship of 3 years go down the drain. that when youve been with a person for that long you tend to do that. that he doesnt love her or care about her anymore but its hard to not mention her. he says it will go away with time but how long until it does? and until then do i just have to suck it up? i know he doesnt love her... there is not doubt in my mind that he loves me but its something that does get on my nerves. what should i do?