Jealousy is something most men experience in varying degrees. It can range from a harmless form of envy to a destructive or violent form psychiatry calls "morbid jealousy." Liane Holliday Willey, Ed.D even puts it on her list of signs he might be dangerous in an article for Psychology Today. Knowing what to look for can help you make more informed decisions about the kind of man you choose. You will need to be as objective as possible about what you are seeing.
He's Too Watchful
If he is always aware of who is looking at you or giving you attention, there might be a problem. This could be real attention or only in his imagination. It is not uncommon for women to be unaware when they are being noticed. However, if he is constantly pointing it out to you and you do not see it, his jealousy may be clouding his perception of those around you. This can make others uncomfortable if they notice the tension.
A jealous man often develops a paranoia about his wife or girlfriend. He asks about the men you work with or maybe checks your phone for men he may or may not know. He could also subtly or not so subtly accuse you of infidelity or even say he believes you will eventually cheat on him. He will insist on knowing your whereabouts at all times. Questioning your honesty about who you were with on girls' night could also be in the mix.
He Has a Strong Commitment to Ideas
When a man possesses an unhealthy level of jealousy, he will demonstrate what Advances in Psychiatric Treatment calls "overvalued ideas." This could be anything he believes to be true which exceeds the boundary of reason. There will be no convincing him he is wrong. For example, if he believes you have been unfaithful, there will be no amount of proof that will deter him from that belief. He may even concoct impossible scenarios to explain away your legitimate arguments.
He's Over Protective
This sign can be easily mistaken for him just wanting you to be safe. What makes it a problem is when his "protectiveness" translates into the verbal or physical confrontation of other men. Men who have made no overt moves to bother you. His reaction will be well outside the bounds of reasonable. This could eventually turn on you. His perception of men's interest in you could morph into his believing you are inviting extra attention. If that happens, you could become the focus of his anger.