The difference between frightened and vulnerable is pretty close. It is usually up to the person feeling it to let you know which one they are experiencing. It may just be a matter of seeing if TM will let you know when you ask him.
HIs other symptoms are unusual but it sounds like it could be anxiety. If he is not getting worse, then it's most likely emotionally related.
As I'm reading your question, one thing seemed to stand out. TM's relationship with women is dysfunctional. The way he relates to you, to other women and the sexual dysfunction you described all point to either some type of abuse by a woman (maybe mother or another significant female in his life) or something abuse related. There are just too many signs to ignore. If I was seeing TM as a patient, it is a path I would explore with him.
The most important sign is probably the dissociation symptoms. If he does not have dissociation, he has signs or mild symptoms of something similar. Dissociation is not easy to diagnose without seeing a person face to face, but it can be possible he has it especially if he was abused. Oftentimes, abused children will remove themselves mentally and emotionally from what is happening in order to survive. Although it is a rare reaction, it does occur in certain cases.
TM may be approaching the other women because of the dysfunction. He either sees them as objects to be feared or he sees them as wanting their love and attention but either way he approaches it in a dysfunctional manner. If he is afraid of them, he may approach them much as an abused child would approach their abuser- seeing them as the only source of comfort but never being able to get any from them. Either way, he is not able to develop normal feelings and therefore tries what he knows and understands in order to attempt to relate.
There is no reason at this point to feel his attempts to engage other women is a threat in any way to your relationship. He has taken a long time to get to the point he is now with you and start over and to be able to do this with another woman would take a lot. The other woman would also have to have your insight and patience and that is quite rare indeed. Plus, you and TM fit together in meeting each others needs. His trust issues, difficulties and the other parts of his situation are not something that can be easily adapted to for most people.
You can choose to react to TM's attempts either by ignoring him when he does this or by letting him know (which sounds like you already did) that it hurts you. I'm not sure at this point if he could stop what he does because it may be based in something deep and unresolved for him. But working with him like you do may help him eventually deal with some of the issues and it may bring about better insight for him.
Let me know if I can help any further,