Jealousness is based on insecurity which, in turn, comes from a poor self image. If a man or woman feels that they could lose the person they feel and believe they are 'in love with,' it is the fear of losing someone they think 'belongs' to them. Not so much a person with a will and mind of their own but an object or possession. An exaggeration perhaps, but it comes close.
On the other hand if you love a person, rather than being 'in love' - which always smacks of not feeling like a full person unless there is such a relationship - you wish them the freedom to be their own person. You grant them the autonomy to which we're all entitled.
Yes, trust comes into it. But if your trust is broken you are not heart-broken. Love is unconditional. So you forgive...I mean really forgive, not say you do and then harbour life-long resentment which pops to the surface whenever the slightest argument occurs.
Being in love is an ego thing; a self-image need. Loving comes from the real self - the Higher Self.
Being 'in love' and being loved back is a wonderful thing; a memorable, life-changing experience. Being in love and feeling that love is not returned can create enormous pain. But moving from being in love to actually loving is far, far more important.