Help! What should I do?

I have been dating a fantastic guy for 4 months, we spend all our time together and are crazily in love, he has even proposed but recently I have been getting insecure about his ex's and the fact he is really gorgeous and puts a lot of weight on appearances. we have been bickering, he is more blunt with me than he used to be and I take it personally and get upset or we disagree on something we see on telly and end up bickering about it, it's really silly and I don't know if this is just a natural progression of the relationship or if we aren't as perfect for each other as we thought we were. I really don't want to mess it up but it's hard to tell who's in teh wrong if anyone at all