I think jealousy has more to do with ownership and selfish desire than with love. I think some jealousy is normal, but I also think that it comes from a place of "this person is mine, and I'm afraid that what they are doing, or how close they are with this another person, means that I will lose them", more than it does love. 

One can be jealous of, for instance, another student in class when said student is praised by the teacher, not because you love your teacher, but because you want to be the favourite student.

It's the same with romantic partners - people think "this is my partner, they should pay attention to me" when they see their partners hanging out with other people. 

Generally, I find that the better communication between the couple, the higher the lever of trust, and the less jealously.

I used to have a friend who no longer talks to me, because he got a girlfriend who thought I would steal him from her, and forbid him from talking to me, or any other female friends. Because of this, I think jealousy definitely isn't love, it's a toxic desire to own your partner.

I believe jealousy is related to mate guarding-- and went to look for something to help explain what I mean.  https://www.ulm.edu/~palmer/JealousyandMate.htm

Jealousy does have some function for protecting the relationship.  One of the parts most interesting about this line of research into mate guarding behavior is this part (from the article linked above):

Based on evolutionary logic, it was predicted that male jealousy would be more concerned with sexual infidelity and female jealousy would be more concerned with emotional infidelity. Buss, Larson, Westen, & Semmelroth (1992) used a series of forced choice experiments to demonstrate that men indicated greater distress to a partner’s sexual, rather than emotional infidelity, whereas women showed the reverse response displaying greater distress to a partner’s emotional infidelity rather than their sexual infidelity.

The above certainly fits with what I have seen as a psychotherapist.  I rarely find men too concerned about the idea of ¨emotional infidelity¨ as long as they believe their partner maintains sexual fidelity, whereas women often ¨go ballistic¨ with jealous about emotional infidelity.  

No, I don't think it's a proof of anything. Still, being a jealous person myself, I'd say I can't imagine love completely without this feeling (I wish I could). I mean, it's not something to be proud of, and of course jealousy can't be a justification for anything along the lines of "Have you prayed tonight?", but I've never been able to avoid it. So, I would say that jealousy by itself doesn't mean much, but, unfortunately, it goes hand in hand with love as I see it.