You are trying to be understanding and accepting of a completely inappropriate situation. It's regretable that your boyfriend ever made this connection when he was drunk and lonely, but for him to be intensifying the connection all this time is completely nuts. No sane girlfriend would put up with this.

Part of your self-esteem - a large part - problem comes from you not realizing that you have rights. I suspect that whoever raised you failed to instill that in you. Your boyfriend, also, may be genuinely confused about what it means to show proper respect for a woman and for a love relationship. So it's up to you to you to decide that this computer activity does absolutely nothing good for the bond of two people living together in love. And it's up to you to role model firm rejection of this behavior.

This is not a case of your boyfriend asserting his right to "have friends." Of course people should have friends, and there are appropriate ways to go about that. What he's doing is not one of those ways. Tell him that it is not okay for him to have lady friends on-line whom he discusses sex with. It is positively, absolutely not okay. Tell him that he is undermining the bond you two have and you want this to stop - now. Also, refuse to listen to anything more that he wants to relate to you about what he discusses with this woman. She's some kind of a nutcase herself.

He's going to have a bunch of arguments about how this is harmless, fun, social activity. Don't get into a debating contest with him because he'll just probably out-talk you. What he's doing is terribly harmful, and the proof is in how you feel. Tell him to knock it off, or you will probably consider leaving him. And tell him to never, ever think he has any right to mail a picture of you to anyone without your permission.