Is this acceptable? Am I crazy?

I have been with my boyfriend almost a ear now, we are very happy and very in love and have what I would describe as a perfect relationship, talking, sharing, honesty, quality time, know everything about each other, fun, able to speak about anything, problem solving, nothing is ever a problem we never fight we just talk things out and sort them asap, were so happy and a perfect match but the thing in the background for me is his ex that he is friends with, she doesn't count as a real ex they haven't been together for 3/4 years and they weren't properly together she lived far away they only met in person once and nothing happened other than a cuddle it was like a cyber relationship really but they were really close through talking and they still talk, she friended me at the beginning of the relationship I didn't like them talking so he deleted her but then they started talking again cos he missed her friendship and so did she thing is shes tried to cause problems for us the whole time being nice to my face then saying or doing something spiteful, shes said hurtful things to me on more than one occasion last time I was so upset cos she tried to split us up by telling me he had told her I embarrass him and loads of other things that he had never ever said and he was furious and had a really go at her but they still talk not as much though, I deleted her and blocked her so she couldn't hurt me anymore and couldn't interfere in our relationship like she has tried to previously but always failed to do cos were strong and know what shes doing, he is aware of her malicious side so takes her with a pinch of salt so she doesn't really bother me anymore the only thing that has bothered me recently after a few months of no problem with them talking is that I saw a message from her with loads of kisses and I explained to him about the kiss rule and that it wasn't appropriate and he didn't know he just thought it polite to respond to what you get first and since then he changed it but I saw 3 recently and I still think that 3 is too many and I guess im just being a bit fanickety, I dont have a problem with them talking I trust him with absolutely my whole heart but I do not trust her and I know he will respond to what she gives him out of politeness but I think that in a casual conversation when they are just friends and he is in a long term serious relationship with future plans she should not be having conversations with more than 1 or 2 kisses or flirting which im sure she probably does and he wont realise cos this is his first real life proper relationship and he doesn't understand the etiquette at all and no he isn't playing dumb he really is just a very sweet caring person and he is just so polite any views would be helpful, its not interfering wit my life or anything its just a little niggle in the back of my mind when I know that they are messaging and im around thanks!

if you dont like their friendship put your foot down,otherwise things may get out of hand and you will lose the person you care

thanks for your reply, I have before told him my feelings and we have discussed and I have been reassured I just sometimes don't know how best to put the problem behind me, most of the time I don't think about it and it doesn't bother me but it was just the kisses thing even though its small that set a little whir in my mind am I overreacting at 3 kisses? I know nothings between them and wont be and I have complete trust she just irritates me more that anything cos I know she would love to split us up but then not want him she just liked that he wasn't with anyone before me so she could wrap him round her finger and that's not the same anymore and that's what gets her she isn't important so she does things annoy me I just need to not let her hes not bothered by her either way she just occassioanlly gets at me any advice on if im overreacting with the kisses or how to forget her completely would be appreciated thanks :)