Avoid doing anything that will make you controlling. Don't tell him to stop texting or talking to her. I have an ex who was jealous about me talking to another ex while he and I were dating, and it got to be a HUGE problem. Just tell him what is bothering you and be honest about why it bothers you. Explaining it well will help him understand why you feel the way you do and he'll be more likely to take what you tell him into consideration.
I deal with jealousy pretty bad mostly because of the nature of the relationship I have. My manfriend and I are not going with the technical term of "dating" for our relationship. For the most part we are monogamous, but we do something like consensual infedelity. If one of us is interested in sex with someone else, we discuss it and ask for permission from the other partner. Thing is, my manfriend is VERY attractive, and this is not just an opinion that I have because I happen to be in a relationship with him. He is a strapping fellow. Now most people know of the status of our relationship, and generally decent people do not attempt to hook up with he or I, but he gets a lot of attention from less-than-reputable girls(aka- really huge sluts). He enjoys the attention he gets from these girls and likes to flirt with them in return even if he isn't interested in them.
Now my jealousy comes from a couple different things. One, I recognize that I am not a bad looking guy myself, but I'm jealous that he gets so much more attention from girls than I do and it almost makes me feel like "the ugly one" of the couple. Two, he changes his behaviour around attractive girls and will refuse affection and will give me minimal attention in their company. And three, even though we do not have the title of "boyfriends", I still feel a sense of commitment to him and he feels the same to me. I honestly don't find many people I am interested in, but he finds plenty and it makes me jealous of these girls when he expresses interest in people other than me.
Also, he identifies as "heteroflexible", meaning that while he is primarily attracted to women, guys are not totally out of the question for him (in the physical sense or in the sense of gender). I have actually noticed that he prefers female-bodied people with masculine personalities and attitudes.
